This CL removes unnecessary code duplication in the fuzzer code. Instead
of having special testing functions to compile and instantiate a
WebAssembly module, we now just call SyncCompile and SyncInstantiate.

This also fixed a problem when the fuzzer generated a GrowMemory
instruction.

BUG=v8:6474
R=clemensh@chromium.org

Change-Id: I5f2f23349b5866ea67be20a0826271791e1a013e
Reviewed-on: https://chromium-review.googlesource.com/529210
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45851}