annotate: simplify annotate parent function The annotate algorithm used a custom parents() function to try to reuse filectx and filelogs. I simplified it a bit to rely more heavily on the self.parents() which makes it work well with alternative filectx implementations. I tested performance on a file with 5000+ revisions but no renames, and on a file with 500 revisions repeating a series of 4 edits+renames and saw zero performance hit. In fact, it was reliably a couple milliseconds faster now. Added the perfannotate command to contrib/perf.py for future use.