Remove obsolete proto breaking-change exception (#11156)

## What changed?
Clean up obsolete buf.yaml ignore

## Why?
Remove temporary ignore that was needed for a known breaking change.

## How did you test it?
- [X] built
- [ ] run locally and tested manually
- [X] covered by existing tests
- [ ] added new unit test(s)
- [ ] added new functional test(s)

proto/internal/buf.yaml

@@ -9,12 +9,6 @@ deps:
 breaking:
   use:
     - WIRE
-  # Uncomment this to temporarily ignore specific files or directories:
-  ignore:
-    # example: - temporal/server/api/.../message.proto
-    # TODO: Remove once this is stable. business_id was intentionally changed from
-    # optional to repeated to support multiple fallback routing fields.
-    - temporal/server/api/routing/v1/extension.proto
 lint:
   use:
     - DEFAULT