rm guard for google3

Bug: skia:
Change-Id: I86495e0fefff2dbd34e39e3a0be891bfc62ec08b
Reviewed-on: https://skia-review.googlesource.com/114581
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
diff --git a/public.bzl b/public.bzl
index d60cf89..fbd005b 100644
--- a/public.bzl
+++ b/public.bzl
@@ -585,7 +585,6 @@
       # Required for building dm.
       "GR_TEST_UTILS",
       # Staging flags for API changes
-      "SK_SUPPORT_LEGACY_BLURMASKFILTER",
       # Should remove after we update golden images
       "SK_WEBP_ENCODER_USE_DEFAULT_METHOD",
       # Experiment to diagnose image diffs in Google3