commit: stop setting rename limit

commit: stop setting rename limit

For its post-commit summary, commit was explicitly setting
the default rename limit to 100. Presumably when the code
was added, it was necessary to do so. These days, however,
it will fall back properly to the diff default, and that
default has long since changed from 100.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>