docs/diffcore: unquote "Complete Rewrites" in headers

docs/diffcore: unquote "Complete Rewrites" in headers

The gitdiffcore documentation quotes the term "Complete Rewrites" in
headers for no real gain. This would make sense if the term could be
easily confused if not properly grouped together. But actually, the term
is quite obvious and thus does not really need any quoting, especially
regarding that it is not used anywhere else.

But more importanly, this brings up a bug when rendering man pages: when
trying to render quotes inside of a section header, we end up with
quotes which have been misaligned to the end of line. E.g.

    diffcore-break: For Splitting Up Complete Rewrites
    --------------------------------------------------

renders as

    DIFFCORE-BREAK: FOR SPLITTING UP  COMPLETE REWRITES""

, which is obviously wrong. While this is fixable for the man pages by
using double-quotes (e.g. ""COMPLETE REWRITES""), this again breaks it
for our generated HTML pages.

So fix the issue by simply dropping quotes inside of section headers,
which is currently only done for the term "Complete Rewrites".

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>