Revert of Implement enableFastMobileScrolling web api. (https://codereview.chromium.org/321473002/)

Reason for revert:
Broke the build.

Original issue's description:
> Implement enableFastMobileScrolling web api.
> 
> The effort needs to be done in 3 steps:
> 1. Create the runtime flag interface in blink;
> 2. Enable the flag for Android from chromium even it does not do anything in blink;
> 3. Replace compile time guard with runtime flag in blink and remove ENABLE_FAST_MOBILE_SCROLLING in gyp file.
> 
> This is the 1st set of changes.
> 
> BUG=381391
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=175621

TBR=tkent@chromium.org,adamk@chromium.org,c.shu@samsung.com
NOTREECHECKS=true
NOTRY=true
BUG=381391

Review URL: https://codereview.chromium.org/317313002

git-svn-id: svn://svn.chromium.org/blink/trunk@175622 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/platform/RuntimeEnabledFeatures.in

@@ -56,7 +56,6 @@ EncryptedMediaAnyVersion status=stable
 ExperimentalCanvasFeatures status=test
 ExperimentalContentSecurityPolicyFeatures status=experimental
 ExperimentalWebSocket status=stable
-FastMobileScrolling
 FileAPIBlobClose status=experimental
 FileConstructor status=experimental
 FileSystem status=stable

third_party/WebKit/Source/web/WebRuntimeFeatures.cpp

@@ -105,11 +105,6 @@ void WebRuntimeFeatures::enableExperimentalCanvasFeatures(bool enable)
     RuntimeEnabledFeatures::setExperimentalCanvasFeaturesEnabled(enable);
 }
 
-void WebRuntimeFeatures::enableFastMobileScrolling(bool enable)
-{
-    RuntimeEnabledFeatures::setFastMobileScrollingEnabled(enable);
-}
-
 void WebRuntimeFeatures::enableFastTextAutosizing(bool enable)
 {
     RuntimeEnabledFeatures::setFastTextAutosizingEnabled(enable);

third_party/WebKit/public/web/WebRuntimeFeatures.h

@@ -58,8 +58,6 @@ public:
 
     BLINK_EXPORT static void enableExperimentalCanvasFeatures(bool);
 
-    BLINK_EXPORT static void enableFastMobileScrolling(bool);
-
     BLINK_EXPORT static void enableFastTextAutosizing(bool);
 
     BLINK_EXPORT static void enableFileSystem(bool);