The FixedArray holding the export wrappers is never being used before
creating the WasmCompiledModule, so there is no need to store it in a
field on the WasmCompilationJob. Just create it when creating the
WasmCompiledModule.

R=ahaas@chromium.org
CC=​mtrofin@chromium.org

Change-Id: Ibdca3d5c58faf4b52df10560bdf2734fdd7a4656
Reviewed-on: https://chromium-review.googlesource.com/758242Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49214}