Remove SkBaseDevice::flush (take 2)

Another small step in removing SkCanvas::flush

Change-Id: I6f3bec367e582754b8463b7bfe6a2542436ca829
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/335647
Commit-Queue: Robert Phillips <robertphillips@google.com>
Reviewed-by: Adlai Holler <adlai@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
diff --git a/RELEASE_NOTES.txt b/RELEASE_NOTES.txt
index d0f918e..3dc29b4 100644
--- a/RELEASE_NOTES.txt
+++ b/RELEASE_NOTES.txt
@@ -37,6 +37,8 @@
     a MTLDevice and MTLCommandQueue is deprecated.
     https://review.skia.org/334426
 
+  * SkCanvas::flush has been deprecated.
+
 * * *
 
 Milestone 88