Remove stale overlay testcase bits

D10V support was removed years ago, but the gdb.base/d10vovly.c file
stayed behind.  Looking a bit closer, I can't find anywhere that
references gdb.base/m32rovly.c either.

Both gdb.base/m32rovly.c and gdb.base/d10vovly.c seem to be older
copies of gdb.base/ovlymgr.c, that are exactly the same, except for
some cosmetic differences, and for missing _ovly_debug_event.  Note
that gdb.base/ovlymgr.c has the #ifdef __M32R__ bits too.  Note also
that gdb.base/overlays.exp is currently only supported on m32r, and
that uses ovlymgr.c not gdb.base/m32rovly.c.

gdb/testsuite/ChangeLog:

	* gdb.base/d10vovly.c: Delete.
	* gdb.base/m32rovly.c: Delete.
	* gdb.base/ovlymgr.c: Remove all code guarded by __D10V__.