Tests: Use script.max_compilations_rate for BWC tests

As the setting is now backported to 6.0, the cluster
formation task can use only the new setting, no need
to use the old one anymore.

buildSrc/src/main/groovy/org/elasticsearch/gradle/test/ClusterFormationTasks.groovy

@@ -329,11 +329,7 @@ class ClusterFormationTasks {
             esConfig['cluster.routing.allocation.disk.watermark.flood_stage'] = '1b'
         }
         // increase script compilation limit since tests can rapid-fire script compilations
-        if (Version.fromString(node.nodeVersion).major > 6) {
-          esConfig['script.max_compilations_rate'] = '2048/1m'
-        } else {
-          esConfig['script.max_compilations_per_minute'] = 2048
-        }
+        esConfig['script.max_compilations_rate'] = '2048/1m'
         esConfig.putAll(node.config.settings)
 
         Task writeConfig = project.tasks.create(name: name, type: DefaultTask, dependsOn: setup)