status/commit: do not suggest "reset HEAD <path>" while merging

status/commit: do not suggest "reset HEAD <path>" while merging

Suggesting "'reset HEAD <path>' to unstage" is dead wrong if we are about
to record a merge commit.  For either an unmerged path (i.e. with
unresolved conflicts), or an updated path, it would result in discarding
what the other branch did.

Note that we do not do anything special in a case where we are amending a
merge.  The user is making an evil merge starting from an already
committed merge, and running "reset HEAD <path>" is the right way to get
rid of the local edit that has been added to the index.

Once "reset --unresolve <path>" becomes available, we might want to
suggest it for a merged path that has unresolve information, but until
then, just remove the incorrect advice.

We might also want to suggest "checkout --conflict <path>" to revert the
file in the work tree to the state of failed automerge for an unmerged
path, but we never did that, and this commit does not change that.

Signed-off-by: Junio C Hamano <gitster@pobox.com>