Revert "Return WebView to 32-bit by default."

This reverts commit 16e049fa.

Reason for revert: No longer need this configuration.

Original change's description:
> Return WebView to 32-bit by default.
> 
> Bug: 1119325
> Change-Id: I04727f349d0012a4a89ab93032530ccecf53e767
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2364210
> Reviewed-by: Richard Coles <torne@chromium.org>
> Commit-Queue: Ben Mason <benmason@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#799739}

TBR=torne@chromium.org,benmason@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 1119325
Change-Id: Ib9b6182502b549a5b4e81aceb8b1370080419fc9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2375647Reviewed-by: Richard Coles <torne@chromium.org>
Reviewed-by: Ben Mason <benmason@chromium.org>
Commit-Queue: Ben Mason <benmason@chromium.org>
Cr-Commit-Position: refs/heads/master@{#801936}

android_webview/nonembedded/BUILD.gn

@@ -190,6 +190,7 @@ jinja_template("trichrome_webview_manifest") {
   variables = trichrome_jinja_variables + _webview_jinja_variables
   if (android_64bit_target_cpu) {
     variables += [
+      "use32bitAbi=",
       "library=libmonochrome_64.so",
       "trichrome_version=$trichrome_64_32_version_code",
     ]