bcachefs: Don't stop copygc while removing devices

With the new backpointer based copygc we don't need an explicit copygc
reserve, we're always evacuating buckets one at a time - so this is no
longer needed, and in fact removing it fixes a deadlock in
bch2_dev_allocator_remove().
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/super.c

@@ -1345,19 +1345,11 @@ static bool bch2_fs_may_start(struct bch_fs *c)
 
 static void __bch2_dev_read_only(struct bch_fs *c, struct bch_dev *ca)
 {
-	/*
-	 * Device going read only means the copygc reserve get smaller, so we
-	 * don't want that happening while copygc is in progress:
-	 */
-	bch2_copygc_stop(c);
-
 	/*
 	 * The allocator thread itself allocates btree nodes, so stop it first:
 	 */
 	bch2_dev_allocator_remove(c, ca);
 	bch2_dev_journal_stop(&c->journal, ca);
-
-	bch2_copygc_start(c);
 }
 
 static void __bch2_dev_read_write(struct bch_fs *c, struct bch_dev *ca)