The mapCommit API is being deprecated because it doesn't run very
fast. Leaving tests around to test how fast it is relative to C Git
isn't instructive. Remove them, which should help aid the transition
away from the mapCommit API.
Change-Id: I27e1c844610d7da5b2c44b33a00602706973c9cc
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>