remove pekko-protobuf depedency

Author: pjfanning

instrumentation/kamon-pekko/build.sbt

@@ -15,7 +15,6 @@ libraryDependencies ++= { if(scalaBinaryVersion.value == "2.11") Seq.empty else
   "org.apache.pekko"   %% "pekko-remote"            % pekkoVersion % "provided,test",
   "org.apache.pekko"   %% "pekko-cluster"           % pekkoVersion % "provided,test",
   "org.apache.pekko"   %% "pekko-cluster-sharding"  % pekkoVersion % "provided,test",
-  "org.apache.pekko"   %% "pekko-protobuf"          % pekkoVersion % "provided,test",
   "org.apache.pekko"   %% "pekko-testkit"           % pekkoVersion % Test
 )}