dm vdo dedupe: switch to using int-map instead of pointer-map

Use get_unaligned_le64() on the hash lock's record name to serve as
the key to use with the int hash-map.

Switching to using int hash-map removes the only consumer of pointer
hash-map, as such it is removed.

Reviewed-by: Matthew Sakai <msakai@redhat.com>
Signed-off-by: Bruce Johnston <bjohnsto@redhat.com>
Signed-off-by: Matthew Sakai <msakai@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>