error_resolve_conflict: drop quotations around operation

When you try to commit with unmerged entries, you get an error like: $ git commit error: 'commit' is not possible because you have unmerged files. The quotes around "commit" are clunky; the user doesn't care that this message is a template with the command-name filled in. Saying: error: commit is not possible because you have unmerged files is easier to read. As this code is called from other places, we may also end up with: $ git merge error: merge is not possible because you have unmerged files $ git cherry-pick foo error: cherry-pick is not possible because you have unmerged files $ git revert foo error: revert is not possible because you have unmerged files All of which look better without the quotes. This also happens to match the behavior of "git pull", which generates a similar message (but does not share code, as it is a shell script). Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>