Add rule to remove x-internal in openapi normalizer #574

Job	Run time
Build sbt/Scala client, servers (samples/client/petstore/java/okhttp-gson)	34s
Build sbt/Scala client, servers (samples/client/petstore/scalaz)	1m 59s
Build sbt/Scala client, servers (samples/client/petstore/scala-pekko)	34s
Build sbt/Scala client, servers (samples/server/petstore/scala-lagom-server)	3m 53s
Build sbt/Scala client, servers (samples/server/petstore/scala-play-server)	4m 40s
Build sbt/Scala client, servers (samples/server/petstore/scala-akka-http-server)	2m 3s
Build sbt/Scala client, servers (samples/server/petstore/scala-pekko-http-server)	39s
Build sbt/Scala client, servers (samples/server/petstore/scalatra)	3m 1s
Build sbt/Scala client, servers (samples/server/petstore/scala-finch)	3m 11s
Build sbt/Scala client, servers (samples/server/petstore/scala-http4s-server)	41s
	21m 15s

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