remove unused device::eraseColor

BUG=skia:
TBR=

Review URL: https://codereview.chromium.org/765643004

include/core/SkDevice.h

@@ -166,9 +166,6 @@ protected:
      */
     virtual void clear(SkColor color) = 0;
 
-    SK_ATTR_DEPRECATED("use clear() instead")
-    void eraseColor(SkColor eraseColor) { this->clear(eraseColor); }
-
     /** These are called inside the per-device-layer loop for each draw call.
      When these are called, we have already applied any saveLayer operations,
      and are handling any looping from the paint, and any effects from the