Remove useless wrappers of asm-generic/rmap.h

xtensa has a header (in its include/asm directory) that is a thin
wrapper around asm-generic/rmap.h. This wrapper is useless, since that
header doesn't exist. It is also unused (no file includes asm/rmap.h).

openrisc generates a similar header at build time (using a generic-y
entry in include/asm/Kbuild). This generated header is useless and
unused too.

Remove this header and this generic-y entry.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Michal Marek <mmarek@suse.cz>