Merge pull request #8386 from paul-elliott-arm/remove_ssl_null_tls12_2_28

[Backport 2.28] Remove NULLing of ssl context in TLS1.2 transform population
diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index 1a2bc7b..6ba3e69 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -992,8 +992,7 @@
     !defined(MBEDTLS_SSL_EXPORT_KEYS) && \
     !defined(MBEDTLS_SSL_DTLS_CONNECTION_ID) && \
     !defined(MBEDTLS_DEBUG_C)
-    ssl = NULL; /* make sure we don't use it except for those cases */
-    (void) ssl;
+    (void) ssl; /* ssl is unused except for those cases */
 #endif
 
     /*