Dependency: update PGV, opencensus-proto, nghttp2, msgpack-c, bazel-gazelle & cleanup (#7787)
Dependency: update PGV, opencensus-proto, nghttp2, msgpack-c, bazel-gazelle & cleanup (#7787)

Update dependencies:

* PGV (changes)
* switch opencensus-proto to 0.2.1 release (changes) /cc @kyessenov
* nghttp2 1.39.1 (release notes 1.39.0, 1.39.1)
* rules_go 0.19.1 (0.19.0 release notes) this is breaking the API only. Reverting to master and will sort out later.
* msgpack-c 3.2.0 (release notes)
* bazel-gazelle 0.18.1 (0.18.0 release notes)
* comment cleanup (remove uneccesary todo and add dates to commits)
* removed unused old backward dependency build file

Risk Level: Medium
Testing: bazel test //test/...

Signed-off-by: Michael Payne <michael@sooper.org>

Mirrored from https://github.com/envoyproxy/envoy @ 07267190c6d8b88ff55c5b9fe607221f7cdcca99

lyft/envoy-api,lyft/envoy-api,lyft/envoy-api