According to the spec, import wrappers are only generated for JavaScript
functions, not for WebAssembly function. If an imported WebAssembly
function does not have the expected type, then a type error is thrown.

R=titzer@chromium.org, rossberg@chromium.org
TEST=mjsunit/wasm/test-import-export-wrapper

Review-Url: https://codereview.chromium.org/2486943005
Cr-Commit-Position: refs/heads/master@{#40901}