MDEV-24125: linux large pages - Revert "Fixed centos 6 build failure"

This reverts commit 6cf8f05f.

Original patch assumed that MAP_HUGETLB as consistent across
achitectures which isn't the case. Defining it unconditionally
broke large pages on every achitecutre where the value differed
from x86_64.

With the EOL for Centos/RHEL6 announced in 10.5.7, <3.8 linux
kernels are no longer supported.

include/my_sys.h

@@ -965,12 +965,6 @@ extern ulonglong my_getcputime(void);
 #define MAP_NORESERVE 0         /* For irix and AIX */
 #endif
 
-/* Compatibility with pre linux 3.8 distributions */
-#ifdef __linux__
-#define MAP_HUGE_SHIFT 26
-#define MAP_HUGETLB 0x40000
-#endif
-
 #ifdef HAVE_MMAP64
 #define my_mmap(a,b,c,d,e,f)    mmap64(a,b,c,d,e,f)
 #else