message: Remove outdated doc about using deprecated-v1
diff: @@ -2,23 +2,3 @@ Protocol buffer definitions for filters.
  Visibility of the definitions should be constrained to none except for
  shared definitions between explicitly enumerated filters (e.g. accesslog and fault definitions).
  -
  -## NOTE
  -
  -If a filter configuration is not captured in the proto specification, you
  -can still supply plain JSON configuration objects for such filters by
  -setting the `"deprecated_v1"` field to true in the filter's
  -configuration. For example,
  -
  -```json
  -{
  - "name": "envoy.rate_limit",
  - "config": {
  - "deprecated_v1": true,
  - "value": {
  - "domain": "some_domain",
  - "timeout_ms": 500
  - }
  - }
  - }
  -```
  