git-gui: Revert "git-gui: Display all authors of git-gui."
This reverts commit 871f4c97ad7e021d1a0a98c80c5da77fcf70e4af.

Too many users have complained about the credits generator in
git-gui, so I'm backing the entire thing out.  This revert will
finish that series.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>