drop the minix_ prefixes for mmap and munmap

also cleanup of various minix-specific changes, cleanup of
mmap-related testing.

Change-Id: I289a4fc50cf8a13df4a6082038d860853a4bd024

libexec/ld.elf_so/xmalloc.c

@@ -60,12 +60,6 @@
  * SUCH DAMAGE.
  */
 
-#ifdef __minix
-/* Minix mmap can do this. */
-#define mmap minix_mmap
-#define munmap minix_munmap
-#endif
-
 #if defined(LIBC_SCCS) && !defined(lint)
 /*static char *sccsid = "from: @(#)malloc.c	5.11 (Berkeley) 2/23/91";*/
 #endif /* LIBC_SCCS and not lint */