Remove GCC redundant-decls workaround for mbedtls_ct_memcmp

Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>

include/mbedtls/constant_time.h

@@ -23,11 +23,6 @@
 
 #include <stddef.h>
 
-#ifdef __GNUC__
-    #pragma GCC diagnostic push
-    #pragma GCC diagnostic ignored "-Wredundant-decls"
-#endif
-
 /** Constant-time buffer comparison without branches.
  *
  * This is equivalent to the standard memcmp function, but is likely to be
@@ -47,8 +42,4 @@ int mbedtls_ct_memcmp(const void *a,
                       const void *b,
                       size_t n);
 
-#ifdef __GNUC__
-    #pragma GCC diagnostic pop
-#endif
-
 #endif /* MBEDTLS_CONSTANT_TIME_H */