Revert "Increase logging on qa:mixed-cluster tests"

This reverts commit e04e5ab037 as we no longer need the increased
logging for the mixed cluster tests. This will reduce the size of logs for some build failures.

qa/mixed-cluster/build.gradle

@@ -45,9 +45,6 @@ for (Version version : versionCollection.versionsWireCompatibleWithCurrent) {
     numNodes = 4
     numBwcNodes = 2
     bwcVersion = version
-
-    setting 'logger.level', 'DEBUG'
-    setting 'logger.org.elasticsearch.discovery', 'TRACE'
   }
 
   Task versionBwcTest = tasks.create(name: "${baseName}#bwcTest") {