Cleanup an ext_proc filter API comments. (#27426)

Signed-off-by: Yanjun Xiang <yanjunxiang@google.com>

Mirrored from https://github.com/envoyproxy/envoy @ dc860e850c577484d31b7b7e3697d6de95cc6d01

envoy/extensions/filters/http/ext_proc/v3/ext_proc.proto

@@ -143,8 +143,9 @@ message ExternalProcessor {
   // a message on the stream that requires a response, it will reset this timer,
   // and will stop processing and return an error (subject to the processing mode)
   // if the timer expires before a matching response is received. There is no
-  // timeout when the filter is running in asynchronous mode. The
-  // ``message_timeout`` range is >= 0s and <= 3600s. Default is 200 milliseconds.
+  // timeout when the filter is running in asynchronous mode. Zero is a valid
+  // config which means the timer will be triggered immediately. If not
+  // configured, default is 200 milliseconds.
   google.protobuf.Duration message_timeout = 7 [(validate.rules).duration = {
     lte {seconds: 3600}
     gte {}
@@ -169,7 +170,6 @@ message ExternalProcessor {
 
   // Specify the upper bound of
   // :ref:`override_message_timeout <envoy_v3_api_field_service.ext_proc.v3.ProcessingResponse.override_message_timeout>`
-  // The ``max_message_timeout`` range is >= 0s and <= 3600s.
   // If not specified, by default it is 0, which will effectively disable the ``override_message_timeout`` API.
   google.protobuf.Duration max_message_timeout = 10 [(validate.rules).duration = {
     lte {seconds: 3600}