MAINTAINERS: remove obsolete file entry in TUN/TAP DRIVER

MAINTAINERS: remove obsolete file entry in TUN/TAP DRIVER

Commit 65eaac591b75 ("um: Remove obsolete legacy network transports")
removes the directory arch/um/os-Linux/drivers/, but misses to remove the
file entry in TUN/TAP DRIVER referring to that directory.

Remove this obsolete file entry. While at it, put the section name in
capital letters.

Signed-off-by: Lukas Bulwahn <lukas.bulwahn@redhat.com>
Reviewed-by: Tiwei Bie <tiwei.btw@antgroup.com>
Link: https://patch.msgid.link/20250507071004.35120-1-lukas.bulwahn@redhat.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>