Remove unused error code MBEDTLS_ERR_SSL_CERTIFICATE_REQUIRED

After the previous commit, the code is no longer used and can be
removed for Mbed TLS 3.0.

Signed-off-by: Hanno Becker <hanno.becker@arm.com>
diff --git a/include/mbedtls/error.h b/include/mbedtls/error.h
index 776013f..73d155b 100644
--- a/include/mbedtls/error.h
+++ b/include/mbedtls/error.h
@@ -108,8 +108,8 @@
  * CIPHER    6   8 (Started from 0x6080)
  * SSL       6   23 (Started from top, plus 0x6000, gaps at
  *                   0x6600)
- * SSL       7   29 (Started from 0x7080, gaps at
- *                   0x7300, 0x7500, 0x7800)
+ * SSL       7   28 (Started from 0x7080, gaps at
+ *                   0x7300, 0x7500, 0x7580, 0x7800)
  *
  * Module dependent error code (5 bits 0x.00.-0x.F8.)
  */
diff --git a/include/mbedtls/ssl.h b/include/mbedtls/ssl.h
index 691b0ee..3ad1927 100644
--- a/include/mbedtls/ssl.h
+++ b/include/mbedtls/ssl.h
@@ -72,7 +72,7 @@
 #define MBEDTLS_ERR_SSL_NO_RNG                            -0x7400  /**< No RNG was provided to the SSL module. */
 #define MBEDTLS_ERR_SSL_NO_CLIENT_CERTIFICATE             -0x7480  /**< No client certification received from the client, but required by the authentication mode. */
 /* NOTE: Error space gap */
-#define MBEDTLS_ERR_SSL_CERTIFICATE_REQUIRED              -0x7580  /**< The own certificate is not set, but needed by the server. */
+/* NOTE: Error space gap */
 #define MBEDTLS_ERR_SSL_PRIVATE_KEY_REQUIRED              -0x7600  /**< The own private key or pre-shared key is not set, but needed. */
 #define MBEDTLS_ERR_SSL_CA_CHAIN_REQUIRED                 -0x7680  /**< No CA Chain is set, but required to operate. */
 #define MBEDTLS_ERR_SSL_UNEXPECTED_MESSAGE                -0x7700  /**< An unexpected message was received from our peer. */