Delete the Layer Squashing runtime feature.

Source/core/testing/InternalSettings.h

Index: Source/core/testing/InternalSettings.h
diff --git a/Source/core/testing/InternalSettings.h b/Source/core/testing/InternalSettings.h
index 616e615423da05bcb95e22e6fc8c0100e696c62f..f1470c7d66d8419a5ee3812eaefb62758bec931a 100644
--- a/Source/core/testing/InternalSettings.h
+++ b/Source/core/testing/InternalSettings.h
@@ -107,10 +107,6 @@ public:
     void setTextAutosizingWindowSizeOverride(int width, int height, ExceptionState&);
     void setViewportEnabled(bool, ExceptionState&);
 
-    // FIXME: This is a temporary flag and should be removed once squashing is
-    // ready (crbug.com/261605).
-    void setLayerSquashingEnabled(bool, ExceptionState&);
-
     // FIXME: The following are RuntimeEnabledFeatures and likely
     // cannot be changed after process start. These setters should
     // be removed or moved onto internals.runtimeFlags: