See if we can clean up lint errors

vars/buildStep.groovy

@@ -1,15 +1,11 @@
 #!/usr/bin/env groovy
 
-import groovy.transform.Field
-
-@Field
+void call(Map config = [:]) {
     Map defaults = [
         saveArtifaces: false,
         buildTest: 'Makefile',
         buildCmd: 'make all'
     ]
-
-def call(Map config = [:]) {
     Map runConfig = defaults + config
     if (runConfig.saveArtifacts) {
         assert runConfig.artifacts : 'Error: saveArtifacts is set to true; must specify artifacts!'