The validation in {ValidateImportWrapperReferencesImmovables} is by now
subsumed by the stricter {WasmCode::Validate}, which is applied to all
WebAssembly code, not just import wrappers.

R=titzer@chromium.org

Change-Id: I8a8cf6e0f07cb289f33b641fe8f674e9698e7f44
Reviewed-on: https://chromium-review.googlesource.com/1099067Reviewed-by: Ben Titzer <titzer@chromium.org>
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53710}