Fix SigningPlugin property is not a file error

Issue gh-208

buildSrc/src/main/java/org/springframework/security/kerberos/gradle/SpringMavenPlugin.java

@@ -22,7 +22,6 @@
 import org.gradle.api.Project;
 import org.gradle.api.attributes.Usage;
 import org.gradle.api.component.AdhocComponentWithVariants;
-import org.gradle.api.component.ConfigurationVariantDetails;
 import org.gradle.api.plugins.JavaPlugin;
 import org.gradle.api.plugins.JavaPluginExtension;
 import org.gradle.api.plugins.PluginManager;
@@ -66,35 +65,15 @@ private void customizeMavenPublication(MavenPublication publication, Project pro
 		customizePom(publication.getPom(), project);
 		project.getPlugins().withType(JavaPlugin.class)
 				.all((javaPlugin) -> customizeJavaMavenPublication(publication, project));
-		suppressMavenOptionalFeatureWarnings(publication);
 	}
 
 	private void customizeJavaMavenPublication(MavenPublication publication, Project project) {
-		addMavenOptionalFeature(project);
 		publication.versionMapping((strategy) -> strategy.usage(Usage.JAVA_API, (mappingStrategy) -> mappingStrategy
 				.fromResolutionOf(JavaPlugin.RUNTIME_CLASSPATH_CONFIGURATION_NAME)));
 		publication.versionMapping(
 				(strategy) -> strategy.usage(Usage.JAVA_RUNTIME, VariantVersionMappingStrategy::fromResolutionResult));
 	}
 
-	private void suppressMavenOptionalFeatureWarnings(MavenPublication publication) {
-		publication.suppressPomMetadataWarningsFor("mavenOptionalApiElements");
-		publication.suppressPomMetadataWarningsFor("mavenOptionalRuntimeElements");
-	}
-
-	private void addMavenOptionalFeature(Project project) {
-		JavaPluginExtension extension = project.getExtensions().getByType(JavaPluginExtension.class);
-		extension.registerFeature("mavenOptional",
-				(feature) -> feature.usingSourceSet(extension.getSourceSets().getByName("main")));
-		AdhocComponentWithVariants javaComponent = (AdhocComponentWithVariants) project.getComponents()
-				.findByName("java");
-		if (javaComponent != null) {
-			javaComponent.addVariantsFromConfiguration(
-				project.getConfigurations().findByName("mavenOptionalRuntimeElements"),
-				ConfigurationVariantDetails::mapToOptional);
-		}
-	}
-
 	private void customizePom(MavenPom pom, Project project) {
 		pom.getUrl().set("https://github.com/spring-projects/spring-security-kerberos");
 		pom.getName().set(project.provider(project::getName));