This reverts commit 8ba517e1.

Reason for revert: causing Chromium test failures on external/wpt/wasm/jsapi/functions/entry-different-function-realm.html, e.g. here: https://ci.chromium.org/p/v8/builders/ci/V8%20Blink%20Mac/3045

Original change's description:
> [wasm] Make an "incumbent context" available for module instantiation
> 
> A Wasm module's start function might be imported from JavaScript, and
> as such might contain calls to Blink. For such a case, we must make
> sure that an "incumbent context" is available.
> See microtask queue handling for a similar example.
> 
> Bug: chromium:1096558
> Change-Id: I2e3c0fc20d4e3581e490822c3ac63ce2c5e1e990
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2284982
> Reviewed-by: Toon Verwaest <verwaest@chromium.org>
> Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#68760}

TBR=jkummerow@chromium.org,verwaest@chromium.org

Change-Id: Ib36d2198cf686f561a2a64034faf0479686f3500
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: chromium:1096558
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2290853Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68775}