Revert r326710 "Fuzzer: remove temporary files after we're done with them."

This broke some Windows buildbots; see llvm-commits thread.

> These were just copies of the relevant fuzzer binary with (presumably)
> meaningful suffixes, but accounted for more than 10% of my build
> directory (> 8GB). Hard drive space is cheap, but not that cheap.

(Also reverts follow-up r326710 which didn't help.)

llvm-svn: 327266