remove unused maskfilter helpers: Combine, Compose

Change-Id: I8c6bf2c3539905c9c7bc9c29454322dbf944fe96
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/287823
Commit-Queue: Mike Reed <reed@google.com>
Reviewed-by: Florin Malita <fmalita@chromium.org>
diff --git a/RELEASE_NOTES.txt b/RELEASE_NOTES.txt
index fbb8b60..11dac99 100644
--- a/RELEASE_NOTES.txt
+++ b/RELEASE_NOTES.txt
@@ -8,6 +8,9 @@
 
   * <insert new release note here>
 
+  * Remove unused SkMaskFilter helpers: compbine, compose
+    Note: shadermaskfilter will likely be removed next (clipShader should serve)
+
   * Add back SkCanvas::kPreserveLCDText_SaveLayerFlag to indicate that saveLayer()
     will preserve LCD-text. All text in the layer must be drawn on opaque background
     to ensure correct rendering.