The test TestExportImportedMemoryGrowMultipleInstances in
test/mjsunit/wasm/import-memory.js had a TODO about not taking into
account the maximum size for exported memory objects, thus permitting to
grow past thhe maximum specified in the exported memory object.

The check is already in place at wasm-objects.cc:266
(https://cs.chromium.org/chromium/src/v8/src/wasm/wasm-objects.cc?rcl=a01b55b548add5aec1d3d4d8fcdadfa01555c6ea&l=266).

This CL removes the TODO and asserts that growing past maximum for
exported objects fails.

R=ahaas@chromium.org, gdeepti@chromium.org

Change-Id: Ifa69e4e85e04bc2280b629cebb30d400cca9420f
Reviewed-on: https://chromium-review.googlesource.com/593948Reviewed-by: Deepti Gandluri <gdeepti@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Enrico Bacis <enricobacis@google.com>
Cr-Commit-Position: refs/heads/master@{#47029}