openrisc: remove unused __ARCH_HAVE_MMU define

The __ARCH_HAVE_MMU define is (and was) used nowhere in the tree and
also doesn't appear to be used by any libc.
Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
Signed-off-by: Stafford Horne <shorne@gmail.com>

arch/openrisc/include/uapi/asm/unistd.h

@@ -17,8 +17,6 @@
  * (at your option) any later version.
  */
 
-#define __ARCH_HAVE_MMU
-
 #define sys_mmap2 sys_mmap_pgoff
 
 #define __ARCH_WANT_RENAMEAT