deprecate engine ci yaml roller (#160682)

This is no longer working after the monorepo merge:
flutter/flutter#160670.

That issue tracks instead teaching the `Linux ci_yaml flutter roller` to
roll both sets of configurations.

Author: christopherfujino

engine/src/flutter/.ci.yaml

@@ -558,9 +558,3 @@ targets:
     timeout: 120
     properties:
       config_name: windows_unopt
-
-  - name: Linux ci_yaml engine roller
-    bringup: true
-    recipe: infra/ci_yaml
-    properties:
-      backfill: "false"