Remove uniqueID from all filter serialization.

(This is essentially a revert of https://codereview.chromium.org/503833002/.)

This was necessary back when SkPaint was flattened even for in-process use. Now that we only flatten SkPaint for cross-process use, there's no need to serialize UniqueIDs.

Note: SkDropShadowImageFilter is being constructed with a croprect and UniqueID (of 0) in Blink. I've made the uniqueID param default to 0 temporarily, until this rolls in and Blink can be changed. (Blink can't be changed first, since unlike the other filters, there's no constructor that takes a cropRect but not a uniqueID.)

BUG=skia:

Review URL: https://codereview.chromium.org/1019493002
diff --git a/src/effects/SkMorphologyImageFilter.cpp b/src/effects/SkMorphologyImageFilter.cpp
index d2ec036..32d525a 100644
--- a/src/effects/SkMorphologyImageFilter.cpp
+++ b/src/effects/SkMorphologyImageFilter.cpp
@@ -24,9 +24,8 @@
 SkMorphologyImageFilter::SkMorphologyImageFilter(int radiusX,
                                                  int radiusY,
                                                  SkImageFilter* input,
-                                                 const CropRect* cropRect,
-                                                 uint32_t uniqueID)
-    : INHERITED(1, &input, cropRect, uniqueID), fRadius(SkISize::Make(radiusX, radiusY)) {
+                                                 const CropRect* cropRect)
+    : INHERITED(1, &input, cropRect), fRadius(SkISize::Make(radiusX, radiusY)) {
 }
 
 void SkMorphologyImageFilter::flatten(SkWriteBuffer& buffer) const {
@@ -254,14 +253,14 @@
     SK_IMAGEFILTER_UNFLATTEN_COMMON(common, 1);
     const int width = buffer.readInt();
     const int height = buffer.readInt();
-    return Create(width, height, common.getInput(0), &common.cropRect(), common.uniqueID());
+    return Create(width, height, common.getInput(0), &common.cropRect());
 }
 
 SkFlattenable* SkDilateImageFilter::CreateProc(SkReadBuffer& buffer) {
     SK_IMAGEFILTER_UNFLATTEN_COMMON(common, 1);
     const int width = buffer.readInt();
     const int height = buffer.readInt();
-    return Create(width, height, common.getInput(0), &common.cropRect(), common.uniqueID());
+    return Create(width, height, common.getInput(0), &common.cropRect());
 }
 
 #ifndef SK_IGNORE_TO_STRING