Revert "diff-delta: produce optimal pack data"

Revert "diff-delta: produce optimal pack data"

This reverts 6b7d25d97bdb8a26719f90d17ff5c9720be68762 commit.

It turns out that the new algorithm has a really bad corner
case, that literally spends minutes for inputs that takes less
than a quater seconds to delta with the old algorithm.  The
resulting delta is 50% smaller which is admirable, but the
performance degradation is simply unacceptable for unconditional
use.

Some example cases are these blobs in Linux 2.6 repository:

    4917ec509720a42846d513addc11cbd25e0e3c4f
    9af06ba723df75fed49f7ccae5b6c9c34bc5115f
    dfc9cd58dc065d17030d875d3fea6e7862ede143

Signed-off-by: Junio C Hamano <junkio@cox.net>