bcachefs: Kill io_in_flight semaphore

This used to be needed more for buffered IO, but now the block layer has
writeback throttling - we can delete this now.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/fs-io.c

@@ -1214,8 +1214,6 @@ static void bch2_writepage_io_done(struct bch_write_op *op)
 	struct bio_vec *bvec;
 	unsigned i;
 
-	up(&io->op.c->io_in_flight);
-
 	if (io->op.error) {
 		set_bit(EI_INODE_ERROR, &io->inode->ei_flags);
 
@@ -1278,8 +1276,6 @@ static void bch2_writepage_do_io(struct bch_writepage_state *w)
 {
 	struct bch_writepage_io *io = w->io;
 
-	down(&io->op.c->io_in_flight);
-
 	w->io = NULL;
 	closure_call(&io->op.cl, bch2_write, NULL, NULL);
 }