Especially "invalid function" and "invalid type" could contain much
more information.

Drive-by: Remove unused WasmTrapInvalidIndex.

R=ahaas@chromium.org

Change-Id: I7fd72c095eaad94e3e2d9bfe6ab4a9ce0bb4798b
Reviewed-on: https://chromium-review.googlesource.com/897526Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51059}