protodoc: single source-of-truth for doc protos. (#8132)

This avoids having to list new docs protos in both docs/build.sh and
api/docs/BUILD. This technical debt cleanup is helpful in v3 proto work
to simplify collecting proto artifacts from a Bazel aspect.

Risk level: Low
Testing: docs/build.sh, visual inspection of docs.

Signed-off-by: Harvey Tuch <htuch@google.com>

Mirrored from https://github.com/envoyproxy/envoy @ b06e2b5c473b4b88e23ed66abd501e29f6bddbee

CONTRIBUTING.md

@@ -8,7 +8,7 @@ API changes are regular PRs in https://github.com/envoyproxy/envoy for the API/c
 changes. They may be as part of a larger implementation PR. Please follow the standard Bazel and CI
 process for validating build/test sanity of `api/` before submitting a PR.
 
-*Note: New .proto files should be also included to [build.sh](https://github.com/envoyproxy/envoy/blob/master/docs/build.sh) and
+*Note: New .proto files should be added to
 [BUILD](https://github.com/envoyproxy/envoy/blob/master/api/docs/BUILD) in order to get the RSTs generated.*
 
 ## Documentation changes

docs/BUILD

@@ -7,8 +7,7 @@ package_group(
     ],
 )
 
-# TODO(htuch): Grow this to cover everything we want to generate docs for, so we can just invoke
-# bazel build //docs:protos --aspects tools/protodoc/protodoc.bzl%proto_doc_aspect  --output_groups=rst
+# This is where you add protos that will participate in docs RST generation.
 proto_library(
     name = "protos",
     deps = [
@@ -94,8 +93,6 @@ proto_library(
         "//envoy/service/auth/v2:external_auth",
         "//envoy/service/discovery/v2:ads",
         "//envoy/service/discovery/v2:rtds",
-        "//envoy/service/load_stats/v2:lrs",
-        "//envoy/service/metrics/v2:metrics_service",
         "//envoy/service/ratelimit/v2:rls",
         "//envoy/service/tap/v2alpha:common",
         "//envoy/type:percent",