[libclc] Remove unnecessary clcmacros.h (llvm#137149)

The macros defined by this file (not to be confused with clcmacro.h)
don't appear necessary for building libclc.

The language version macros should be handled by clang, and there are no
uses of NULL or kernel_exec in the source code.

Author: frasercrmck

libclc/generic/include/clc/clc.h

@@ -35,9 +35,6 @@
 /* 6.2.4.2 Reinterpreting Types Using as_type() and as_typen() */
 #include <clc/as_type.h>
 
-/* 6.9 Preprocessor Directives and Macros */
-#include <clc/clcmacros.h>
-
 /* 6.11.1 Work-Item Functions */
 #include <clc/workitem/get_global_size.h>
 #include <clc/workitem/get_global_id.h>