Remove unecessary import in notification protobuf file

sonar-ws/src/main/protobuf/ws-notifications.proto

@@ -20,8 +20,6 @@ syntax = "proto2";
 
 package sonarqube.ws.notification;
 
-import "ws-commons.proto";
-
 option java_package = "org.sonarqube.ws";
 option java_outer_classname = "Notifications";
 option optimize_for = SPEED;