reset_head(): remove action parameter

The only use of the action parameter is to setup the error messages
for unpack_trees(). All but two cases pass either "checkout" or
"reset". The case that passes "reset --hard" would be better passing
"reset" so that the error messages match the builtin reset command
like all the other callers that are doing a reset. The case that
passes "Fast-forwarded" is only updating HEAD and so the parameter is
unused in that case as it does not call unpack_trees(). The value to
pass to setup_unpack_trees_porcelain() can be determined by checking
whether flags contains RESET_HEAD_HARD without the caller having to
specify it.

Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/reset.c b/reset.c
index 3537de9..7841b2b 100644
--- a/reset.c
+++ b/reset.c
@@ -8,7 +8,7 @@
 #include "tree.h"
 #include "unpack-trees.h"
 
-int reset_head(struct repository *r, struct object_id *oid, const char *action,
+int reset_head(struct repository *r, struct object_id *oid,
 	       const char *switch_to_branch, unsigned flags,
 	       const char *reflog_orig_head, const char *reflog_head,
 	       const char *default_reflog_action)
@@ -23,7 +23,7 @@ int reset_head(struct repository *r, struct object_id *oid, const char *action,
 	struct lock_file lock = LOCK_INIT;
 	struct unpack_trees_options unpack_tree_opts = { 0 };
 	struct tree *tree;
-	const char *reflog_action;
+	const char *action, *reflog_action;
 	struct strbuf msg = STRBUF_INIT;
 	size_t prefix_len;
 	struct object_id *old_orig = NULL, oid_old_orig;
@@ -50,6 +50,7 @@ int reset_head(struct repository *r, struct object_id *oid, const char *action,
 	if (refs_only)
 		goto reset_head_refs;
 
+	action = reset_hard ? "reset" : "checkout";
 	setup_unpack_trees_porcelain(&unpack_tree_opts, action);
 	unpack_tree_opts.head_idx = 1;
 	unpack_tree_opts.src_index = r->index;