Remove ciphersuite from SSL config if single suite hardcoded

If MBEDTLS_SSL_SINGLE_CIPHERSUITE is enabled, it overwrites
the runtime configuration of supported ciphersuites, which
includes both the configuration API and the fields which are
used to store the configuration. Both are therefore no longer
needed and should be removed for the benefit of code-size,
memory usage, and API clarity (no accidental hiccup of runtime
vs. compile-time configuration possible).

The configuration API mbedtls_ssl_conf_ciphersuites() has
already been removed in case MBEDTLS_SSL_SINGLE_CIPHERSUITE,
and this commit removes the field

  mbedtls_ssl_config::ciphersuite_list

which it updates.
diff --git a/include/mbedtls/ssl.h b/include/mbedtls/ssl.h
index c72bbeb..f9b9502 100644
--- a/include/mbedtls/ssl.h
+++ b/include/mbedtls/ssl.h
@@ -972,7 +972,9 @@
      * Pointers
      */
 
+#if !defined(MBEDTLS_SSL_SINGLE_CIPHERSUITE)
     const int *ciphersuite_list[4]; /*!< allowed ciphersuites per version   */
+#endif /* MBEDTLS_SSL_SINGLE_CIPHERSUITE */
 
     /** Callback for printing debug output                                  */
     void (*f_dbg)(void *, int, const char *, int, const char *);
@@ -2466,6 +2468,7 @@
  */
 const mbedtls_ssl_session *mbedtls_ssl_get_session_pointer( const mbedtls_ssl_context *ssl );
 
+#if !defined(MBEDTLS_SSL_SINGLE_CIPHERSUITE)
 /**
  * \brief               Set the list of allowed ciphersuites and the preference
  *                      order. First in the list has the highest preference.
@@ -2478,11 +2481,43 @@
  *                      over the preference of the client unless
  *                      MBEDTLS_SSL_SRV_RESPECT_CLIENT_PREFERENCE is defined!
  *
+ * \note                On constrained systems, support for a single ciphersuite
+ *                      (in all versions) can be fixed at compile-time through
+ *                      the configuration option MBEDTLS_SSL_SINGLE_CIPHERSUITE.
+ *
  * \param conf          SSL configuration
  * \param ciphersuites  0-terminated list of allowed ciphersuites
  */
 void mbedtls_ssl_conf_ciphersuites( mbedtls_ssl_config *conf,
-                                   const int *ciphersuites );
+                                    const int *ciphersuites );
+
+/**
+ * \brief               Set the list of allowed ciphersuites and the
+ *                      preference order for a specific version of the protocol.
+ *                      (Only useful on the server side)
+ *
+ *                      The ciphersuites array is not copied, and must remain
+ *                      valid for the lifetime of the ssl_config.
+ *
+ * \param conf          SSL configuration
+ * \param ciphersuites  0-terminated list of allowed ciphersuites
+ * \param major         Major version number (only MBEDTLS_SSL_MAJOR_VERSION_3
+ *                      supported)
+ * \param minor         Minor version number (MBEDTLS_SSL_MINOR_VERSION_0,
+ *                      MBEDTLS_SSL_MINOR_VERSION_1 and MBEDTLS_SSL_MINOR_VERSION_2,
+ *                      MBEDTLS_SSL_MINOR_VERSION_3 supported)
+ *
+ * \note                With DTLS, use MBEDTLS_SSL_MINOR_VERSION_2 for DTLS 1.0
+ *                      and MBEDTLS_SSL_MINOR_VERSION_3 for DTLS 1.2
+ *
+ * \note                On constrained systems, support for a single ciphersuite
+ *                      (in all versions) can be fixed at compile-time through
+ *                      the configuration option MBEDTLS_SSL_SINGLE_CIPHERSUITE.
+ */
+void mbedtls_ssl_conf_ciphersuites_for_version( mbedtls_ssl_config *conf,
+                                       const int *ciphersuites,
+                                       int major, int minor );
+#endif /* !MBEDTLS_SSL_SINGLE_CIPHERSUITE */
 
 #define MBEDTLS_SSL_UNEXPECTED_CID_IGNORE 0
 #define MBEDTLS_SSL_UNEXPECTED_CID_FAIL   1
@@ -2531,29 +2566,6 @@
           !MBEDTLS_SSL_CONF_CID_LEN &&
           !MBEDTLS_SSL_CONF_IGNORE_UNEXPECTED_CID */
 
-/**
- * \brief               Set the list of allowed ciphersuites and the
- *                      preference order for a specific version of the protocol.
- *                      (Only useful on the server side)
- *
- *                      The ciphersuites array is not copied, and must remain
- *                      valid for the lifetime of the ssl_config.
- *
- * \param conf          SSL configuration
- * \param ciphersuites  0-terminated list of allowed ciphersuites
- * \param major         Major version number (only MBEDTLS_SSL_MAJOR_VERSION_3
- *                      supported)
- * \param minor         Minor version number (MBEDTLS_SSL_MINOR_VERSION_0,
- *                      MBEDTLS_SSL_MINOR_VERSION_1 and MBEDTLS_SSL_MINOR_VERSION_2,
- *                      MBEDTLS_SSL_MINOR_VERSION_3 supported)
- *
- * \note                With DTLS, use MBEDTLS_SSL_MINOR_VERSION_2 for DTLS 1.0
- *                      and MBEDTLS_SSL_MINOR_VERSION_3 for DTLS 1.2
- */
-void mbedtls_ssl_conf_ciphersuites_for_version( mbedtls_ssl_config *conf,
-                                       const int *ciphersuites,
-                                       int major, int minor );
-
 #if defined(MBEDTLS_X509_CRT_PARSE_C)
 /**
  * \brief          Set the X.509 security profile used for verification