In https://chromium-review.googlesource.com/c/505614/ I added code to
the test runner which deletes the old corpus of the wasm fuzzer. It's
time now to remove this code again.

R=machenbach@chromium.org

Change-Id: Ic3b8f7a1f6d725f0bf070b404a75ac37551a07c0
Reviewed-on: https://chromium-review.googlesource.com/519405Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45641}