AnnotationProcessors shouldn't set the SourceVersion unless required

The version for MethodCompletionProviderProcessor is automatically
in its superclass LayerGeneratingProcessor.

this resolves warnings like:
warning: Supported source version 'RELEASE_7' from annotation processor
'o.n.m.l.n.p.MethodCompletionProviderProcessor' less than -source '8'.

or:
warning: Supported source version 'RELEASE_8' from annotation processor
'org.netbeans.modules.java.source.TreeShimsCopier' less than -source '11'

php/languages.neon/src/org/netbeans/modules/languages/neon/processors/MethodCompletionProviderProcessor.java

@@ -22,8 +22,6 @@
 import javax.annotation.processing.Processor;
 import javax.annotation.processing.RoundEnvironment;
 import javax.annotation.processing.SupportedAnnotationTypes;
-import javax.annotation.processing.SupportedSourceVersion;
-import javax.lang.model.SourceVersion;
 import javax.lang.model.element.Element;
 import javax.lang.model.element.TypeElement;
 import org.netbeans.modules.languages.neon.completion.CompletionProviders;
@@ -37,7 +35,6 @@
  * @author Ondrej Brejla <[email protected]>
  */
 @ServiceProvider(service = Processor.class)
-@SupportedSourceVersion(SourceVersion.RELEASE_7)
 @SupportedAnnotationTypes("org.netbeans.modules.languages.neon.spi.completion.MethodCompletionProvider.Registration")
 public class MethodCompletionProviderProcessor extends LayerGeneratingProcessor {