Use `OptionalUtil` instead of methods in `org.apache.pekko.http.impl.util.Util`

[mdedetrich]

Methods from

pekko-http/http-core/src/main/java/org/apache/pekko/http/impl/util/Util.java

Line 30 in 4833a8e

public abstract class Util {

have been copied to pekko core in apache/pekko#2464. When pekko 2.0.0-M1 has been published and pekko-http starts depending on this artifact we should use those methods in OptionalUtil and delete the ones in Util