webview: remove obsolete workaround for API <=23

On API24+ the implementation of WebViewDelegate.addWebViewAssetPath in
the framework no longer calls getAssets() on the context that's been
passed to it (it only uses getApplicationInfo()) so the workaround of
passing a ContextWrapper here to override getAssets() is obsolete now
that we no longer support API23 and below.

Fixed: 1382959
Change-Id: I63fc60784f5509253012a03381a6f28db87c63d7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5017449
Reviewed-by: Nate Fischer <ntfschr@chromium.org>
Auto-Submit: Richard (Torne) Coles <torne@chromium.org>
Commit-Queue: Nate Fischer <ntfschr@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1223146}