drop the minix_ prefixes for mmap and munmap

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

Change-Id: I289a4fc50cf8a13df4a6082038d860853a4bd024

lib/libc/include/namespace.h

@@ -923,8 +923,8 @@
 #define truncate _truncate
 #define write _write
 #define writev _writev
-#define minix_mmap _minix_mmap
-#define minix_munmap _minix_munmap
+#define mmap _mmap
+#define munmap _munmap
 #define vfork __vfork14
 #endif /* __minix */