Revert "Enable mojo based synchronous compositor"

This reverts commit 69ac9fe8.

Reason for revert: Caused crbug.com/816538, which is a crash causing
test flakes.
Bug: 816538

Original change's description:
> Enable mojo based synchronous compositor
> 
> Turn off disabling mojo input messages for webview. That will enable
> the mojo input channel and the mojo synchronous compositor input channel.
> 
> BUG=722928
> 
> Change-Id: I14ae3d3a83405eb9c6a228f7f08171dab3ca86f2
> Reviewed-on: https://chromium-review.googlesource.com/898553
> Commit-Queue: Dave Tapuska <dtapuska@chromium.org>
> Reviewed-by: Bo <boliu@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#539127}

TBR=boliu@chromium.org,dtapuska@chromium.org

Change-Id: Ic0b24d2fb2d68366f9ce5a7a25daab06ef387c7f
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 722928
Reviewed-on: https://chromium-review.googlesource.com/937781Reviewed-by: Bo <boliu@chromium.org>
Commit-Queue: Bo <boliu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#539173}

android_webview/lib/aw_main_delegate.cc

@@ -157,6 +157,8 @@ bool AwMainDelegate::BasicStartupComplete(int* exit_code) {
   CommandLineHelper::AddDisabledFeature(*cl,
                                         media::kMediaDrmPersistentLicense.name);
 
+  CommandLineHelper::AddDisabledFeature(*cl, features::kMojoInputMessages.name);
+
   CommandLineHelper::AddEnabledFeature(
       *cl, autofill::features::kAutofillSkipComparingInferredLabels.name);