Removed obsolete step in for rolling a new engine

CONTRIBUTING.md

@@ -257,15 +257,6 @@ few steps:
    a new version is important in order to not break folks using prebuilt
    binaries in their workflow (e.g., our customers).
 
-3. Land a change that update our dependency on the `sky_engine` and
-   `sky_services` packages to point to the new version of the engine that you
-   just published. These dependencies are defined by [packages/flutter/pubspec.yaml](packages/flutter/pubspec.yaml).
-   After changing the `pubspec.yaml` file, you'll need to run
-   `./dev/update_packages.dart` to update all the packages in this repository to
-   see the new dependency. As part of landing this change, you should make
-   whatever other changes are needed in this repository to account for your
-   breaking change.
-
 API docs for master branch
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