bcachefs: Delete an incorrect bch2_trans_unlock()

These deletes a bch2_trans_unlock() call from __bch2_move_data(). It was
redundant; bch2_move_extent() has the correct unlock call, and it was
buggy because when move_extent calls bch2_extent_drop_ptrs() we don't
want the transaction to be unlocked yet - this fixes a btree_iter.c
assertion.

Fixes https://github.com/koverstreet/bcachefs/issues/511.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/move.c

@@ -583,7 +583,6 @@ static int __bch2_move_data(struct moving_context *ctxt,
 		 */
 		bch2_bkey_buf_reassemble(&sk, c, k);
 		k = bkey_i_to_s_c(sk.k);
-		bch2_trans_unlock(&trans);
 
 		ret2 = bch2_move_extent(&trans, &iter, ctxt, NULL,
 					io_opts, btree_id, k, data_opts);