log-tree: drop unused commit param in remerge_diff()

This function has never used its "commit" parameter since it was added
in db757e8 (show, log: provide a --remerge-diff capability,
2022-02-02).

This makes sense; we already have separate parameters for the parents
(which lets us redo the merge) and the oid of the result tree (which we
can then diff against the remerge result).

Let's drop the unused parameter in the name of clarity.

Signed-off-by: Jeff King <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: peff

log-tree.c

@@ -956,8 +956,7 @@ static void cleanup_additional_headers(struct diff_options *o)
 
 static int do_remerge_diff(struct rev_info *opt,
 			   struct commit_list *parents,
-			   struct object_id *oid,
-			   struct commit *commit)
+			   struct object_id *oid)
 {
 	struct merge_options o;
 	struct commit_list *bases;
@@ -1052,7 +1051,7 @@ static int log_tree_diff(struct rev_info *opt, struct commit *commit, struct log
 					"for octopus merges.\n");
 				return 1;
 			}
-			return do_remerge_diff(opt, parents, oid, commit);
+			return do_remerge_diff(opt, parents, oid);
 		}
 		if (opt->combine_merges)
 			return do_diff_combined(opt, commit);