btrfs: zoned: remove left over ASSERT checking for single profile

With commit dcf5652291f6 ("btrfs: zoned: allow DUP on meta-data block
groups") we started allowing DUP on metadata block groups, so the
ASSERT()s in btrfs_can_activate_zone() and btrfs_zoned_get_device() are
no longer valid and in fact even harmful.

Fixes: dcf5652291f6 ("btrfs: zoned: allow DUP on meta-data block groups")
CC: stable@vger.kernel.org # 5.17
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>