trydiff: make addindexmeta() unconditionally add index meta The conditional-ness is not clear from the name and there is only one caller, so it's clearer to check on the call site. Moving it also makes addindexmeta() no longer close on the 'opts' variable.

trydiff: remove unused code for git index of "combined diff" We only ever produce diffs with one pre- and one post-image, so remove the code for displaying "index" lines for combined diffs.