Fix define for ssl_conf_curves()

This is a security feature, it shouldn't be optional.
diff --git a/include/mbedtls/compat-1.3.h b/include/mbedtls/compat-1.3.h
index 8a3ab96..0af0a9e 100644
--- a/include/mbedtls/compat-1.3.h
+++ b/include/mbedtls/compat-1.3.h
@@ -585,9 +585,6 @@
 #if defined MBEDTLS_SSL_SESSION_TICKETS
 #define POLARSSL_SSL_SESSION_TICKETS MBEDTLS_SSL_SESSION_TICKETS
 #endif
-#if defined MBEDTLS_SSL_SET_CURVES
-#define POLARSSL_SSL_SET_CURVES MBEDTLS_SSL_SET_CURVES
-#endif
 #if defined MBEDTLS_SSL_SRV_C
 #define POLARSSL_SSL_SRV_C MBEDTLS_SSL_SRV_C
 #endif
diff --git a/include/mbedtls/config.h b/include/mbedtls/config.h
index f0d293c..02dd969 100644
--- a/include/mbedtls/config.h
+++ b/include/mbedtls/config.h
@@ -1155,20 +1155,6 @@
 #define MBEDTLS_SSL_TRUNCATED_HMAC
 
 /**
- * \def MBEDTLS_SSL_SET_CURVES
- *
- * Enable mbedtls_ssl_conf_curves().
- *
- * This is disabled by default since it breaks binary compatibility with the
- * 1.3.x line. If you choose to enable it, you will need to rebuild your
- * application against the new header files, relinking will not be enough.
- * It will be enabled by default, or no longer an option, in the 1.4 branch.
- *
- * Uncomment to make mbedtls_ssl_conf_curves() available.
- */
-//#define MBEDTLS_SSL_SET_CURVES
-
-/**
  * \def MBEDTLS_THREADING_ALT
  *
  * Provide your own alternate threading implementation.
diff --git a/include/mbedtls/ssl.h b/include/mbedtls/ssl.h
index 4bca71c..318ca46 100644
--- a/include/mbedtls/ssl.h
+++ b/include/mbedtls/ssl.h
@@ -535,7 +535,7 @@
     mbedtls_x509_crl *ca_crl;       /*!< trusted CAs CRLs                   */
 #endif /* MBEDTLS_X509_CRT_PARSE_C */
 
-#if defined(MBEDTLS_SSL_SET_CURVES)
+#if defined(MBEDTLS_ECP_C)
     const mbedtls_ecp_group_id *curve_list; /*!< allowed curves             */
 #endif
 
@@ -1504,7 +1504,7 @@
                                       unsigned int bitlen );
 #endif /* MBEDTLS_DHM_C && MBEDTLS_SSL_CLI_C */
 
-#if defined(MBEDTLS_SSL_SET_CURVES)
+#if defined(MBEDTLS_ECP_C)
 /**
  * \brief          Set the allowed curves in order of preference.
  *                 (Default: all defined curves.)
@@ -1524,7 +1524,7 @@
  *                 terminated by MBEDTLS_ECP_DP_NONE.
  */
 void mbedtls_ssl_conf_curves( mbedtls_ssl_config *conf, const mbedtls_ecp_group_id *curves );
-#endif /* MBEDTLS_SSL_SET_CURVES */
+#endif /* MBEDTLS_ECP_C */
 
 #if defined(MBEDTLS_X509_CRT_PARSE_C)
 /**
diff --git a/include/mbedtls/ssl_internal.h b/include/mbedtls/ssl_internal.h
index 122c1ee..e074ce2 100644
--- a/include/mbedtls/ssl_internal.h
+++ b/include/mbedtls/ssl_internal.h
@@ -375,7 +375,7 @@
 
 mbedtls_md_type_t mbedtls_ssl_md_alg_from_hash( unsigned char hash );
 
-#if defined(MBEDTLS_SSL_SET_CURVES)
+#if defined(MBEDTLS_ECP_C)
 int mbedtls_ssl_curve_is_acceptable( const mbedtls_ssl_context *ssl, mbedtls_ecp_group_id grp_id );
 #endif