This removes an occurrence where the "%Foo" native syntax appears as part
of a string. Such strings are picked up by the fuzzer and recombined in
unsupported ways, producing false-positive crash reports. Simply avoid
having those strings in the fuzzing corpus.

R=clemensh@chromium.org
TEST=mjsunit/regress/wasm/regress-808848
BUG=chromium:844842

Change-Id: I017c1552578f0d26033e58b11353e87e27a69ebf
Reviewed-on: https://chromium-review.googlesource.com/1136300Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54432}