MAINTAINERS: Remove incorrect M: tag for dm-devel@lists.linux.dev

The dm-devel@lists.linux.dev mailing list should only be listed under
the L: (List) tag in the MAINTAINERS file. However, it was incorrectly
listed under both L: and M: (Maintainers) tags, which is not accurate.
Remove the M: tag for dm-devel@lists.linux.dev in the MAINTAINERS file
to reflect the correct categorization.
Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>

MAINTAINERS

@@ -6157,7 +6157,6 @@ DEVICE-MAPPER  (LVM)
 M:	Alasdair Kergon <agk@redhat.com>
 M:	Mike Snitzer <snitzer@kernel.org>
 M:	Mikulas Patocka <mpatocka@redhat.com>
-M:	dm-devel@lists.linux.dev
 L:	dm-devel@lists.linux.dev
 S:	Maintained
 Q:	http://patchwork.kernel.org/project/dm-devel/list/
@@ -6173,7 +6172,6 @@ F:	include/uapi/linux/dm-*.h
 
 DEVICE-MAPPER VDO TARGET
 M:	Matthew Sakai <msakai@redhat.com>
-M:	dm-devel@lists.linux.dev
 L:	dm-devel@lists.linux.dev
 S:	Maintained
 F:	Documentation/admin-guide/device-mapper/vdo*.rst