router: remove route-action level header manipulation (#6408)

Signed-off-by: Derek Argueta <dereka@pinterest.com>

Mirrored from https://github.com/envoyproxy/envoy @ 26d3aaf394164c35ae19ccac8e9d2317a43f3e35

envoy/api/v2/route/route.proto

@@ -639,14 +639,9 @@ message RouteAction {
   // https://github.com/lyft/protoc-gen-validate/issues/42 is resolved.]
   core.RoutingPriority priority = 11;
 
-  // [#not-implemented-hide:]
-  repeated core.HeaderValueOption request_headers_to_add = 12 [deprecated = true];
-
-  // [#not-implemented-hide:]
-  repeated core.HeaderValueOption response_headers_to_add = 18 [deprecated = true];
-
-  // [#not-implemented-hide:]
-  repeated string response_headers_to_remove = 19 [deprecated = true];
+  reserved 12;
+  reserved 18;
+  reserved 19;
 
   // Specifies a set of rate limit configurations that could be applied to the
   // route.