Mark non-flaky test as such (flutter#60553)

liyuqian · web-flow · commit 84f50d14c35a · 2020-06-29T15:03:03.000-07:00
diff --git a/dev/devicelab/manifest.yaml b/dev/devicelab/manifest.yaml
@@ -759,7 +759,6 @@ tasks:
       with SkSL shader warm-up.
     stage: devicelab
     required_agent_capabilities: ["linux/android"]
-    flaky: true
 
   flutter_gallery__transition_perf_with_semantics:
     description: >
