Fix bug in GrClearOp combining and remove some asserts

The buffer combining code path was combining the ops but never
telling the external system that the second op could be removed.

Bug: skia:10963
Change-Id: If015d877ffbbb75964aae9ca92ea760d7041372a
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/339203
Commit-Queue: Robert Phillips <robertphillips@google.com>
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
diff --git a/src/gpu/ops/GrClearOp.cpp b/src/gpu/ops/GrClearOp.cpp
index 8637b8f..76720a1 100644
--- a/src/gpu/ops/GrClearOp.cpp
+++ b/src/gpu/ops/GrClearOp.cpp
@@ -60,14 +60,13 @@
         // When the scissors are the exact same but the buffers are different, we can combine and
         // clear both stencil and clear together in onExecute().
         if (other->fBuffer & Buffer::kColor) {
-            SkASSERT((fBuffer & Buffer::kStencilClip) && !(fBuffer & Buffer::kColor));
             fColor = other->fColor;
         }
         if (other->fBuffer & Buffer::kStencilClip) {
-            SkASSERT(!(fBuffer & Buffer::kStencilClip) && (fBuffer & Buffer::kColor));
             fStencilInsideMask = other->fStencilInsideMask;
         }
         fBuffer = Buffer::kBoth;
+        return CombineResult::kMerged;
     }
     return CombineResult::kCannotCombine;
 }