message: envoy_build_system: remove unused build macro
  This build macro is private (_) and unused in envoy_build_system.bzl.
  Risk Level: Low
  Testing: Ran bazel test //test/common/... //test/exe/...
diff: @@ -603,11 +603,6 @@ def envoy_sh_test(
  **kargs
  )
  -def _proto_header(proto_path):
  - if proto_path.endswith(".proto"):
  - return proto_path[:-5] + "pb.h"
  - return None
  -
  # Envoy proto targets should be specified with this function.
  def envoy_proto_library(name, external_deps = [], **kwargs):
  external_proto_deps = []
  