As part of #8082, we introduced shadow protos for Envoy internal use (see https://docs.google.com/document/d/1mGO9LtVo7t4Lph7WlmyGCxXye3h6j29z3JZvIBbs_D0/edit# for rationale).

Ultimately, we should not be checking into the repository these generated artifacts. If we want to keep shadowing (for convenience), we should be using protoxform to generate the desired shadows prior to invoking PGV, to generate shadows.

Preferably, we handle future deprecations without the need for shadowing, in v4+.