Remove custom String URL encoder in Gerrit-verifier-change.groovy

The String.metaClass.encodeURL-method is not used in the script anymore.
Thus this change removes the custom implementation that was still
present in the script.

Change-Id: Iff1145ca71e92de84db59a735aa59b44cea19687
diff --git a/jenkins/gerrit-verifier-change.groovy b/jenkins/gerrit-verifier-change.groovy
index 99a597a..5f91818 100644
--- a/jenkins/gerrit-verifier-change.groovy
+++ b/jenkins/gerrit-verifier-change.groovy
@@ -19,9 +19,6 @@
 import groovy.json.*
 import java.text.*
 
-String.metaClass.encodeURL = {
-  java.net.URLEncoder.encode(delegate)
-}
 
 class Globals {
   static long curlTimeout = 10000