Remove redundant pragma clang

Clang honors pragma GCC so specifying is is redundant (and with the
right flags GCC somewhat rudely whines about it.)

Author: brooksdavis

test/cbor_serialize_test.c

@@ -6,7 +6,6 @@
  */
 
 // cbor_serialize_alloc
-#pragma clang diagnostic ignored "-Wdeprecated-declarations"
 #pragma GCC diagnostic ignored "-Wdeprecated-declarations"
 
 #include <math.h>