The save comes with an IO overhead which can slow down the rehash loop in bitbake
a lot. We only needed to do this when recipes were doing unihash cache copying. Now
they aren't doing that, drop this IO pain point.
(Bitbake rev: dfc15ef99302dea22a051c9eb8398ffd5cf1fc20)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>