remove stat member aliases from ppc-specific bits/stat.h

if these are to be supported, they belong in the main stat.h, not
repeated for each arch.

arch/powerpc/bits/stat.h

@@ -19,9 +19,3 @@ struct stat
 	struct timespec st_ctim;
 	unsigned __unused[2];
 };
-
-#ifdef _BSD_SOURCE
-#define st_atimespec st_atim
-#define st_mtimespec st_mtim
-#define st_ctimespec st_ctim
-#endif