@SuppressRestrictedWarnings did not need RUNTIME retention

[jglick]

Seems to have been a contributing cause of a Guice error encountered by @schottsfired when an optional dependency was not present in the test classpath:

java.lang.ArrayStoreException: sun.reflect.annotation.TypeNotPresentExceptionProxy
        at sun.reflect.annotation.AnnotationParser.parseClassArray(AnnotationParser.java:724)
        at sun.reflect.annotation.AnnotationParser.parseArray(AnnotationParser.java:531)
        at sun.reflect.annotation.AnnotationParser.parseMemberValue(AnnotationParser.java:355)
        at sun.reflect.annotation.AnnotationParser.parseAnnotation2(AnnotationParser.java:286)
        at sun.reflect.annotation.AnnotationParser.parseAnnotations2(AnnotationParser.java:120)
        at sun.reflect.annotation.AnnotationParser.parseAnnotations(AnnotationParser.java:72)
        at java.lang.Class.createAnnotationData(Class.java:3521)
        at java.lang.Class.annotationData(Class.java:3510)
        at java.lang.Class.getAnnotation(Class.java:3415)
        at com.google.inject.internal.InjectorImpl.createUninitializedBinding(InjectorImpl.java:629)
        at com.google.inject.internal.UntargettedBindingProcessor$1.visit(UntargettedBindingProcessor.java:51)
        at com.google.inject.internal.UntargettedBindingProcessor$1.visit(UntargettedBindingProcessor.java:35)
        at com.google.inject.internal.UntargettedBindingImpl.acceptTargetVisitor(UntargettedBindingImpl.java:41)
        at com.google.inject.internal.UntargettedBindingProcessor.visit(UntargettedBindingProcessor.java:35)
        at com.google.inject.internal.UntargettedBindingProcessor.visit(UntargettedBindingProcessor.java:27)
        at com.google.inject.internal.BindingImpl.acceptVisitor(BindingImpl.java:93)
        at com.google.inject.internal.AbstractProcessor.process(AbstractProcessor.java:56)
        at com.google.inject.internal.InjectorShell$Builder.build(InjectorShell.java:187)
        at com.google.inject.internal.InternalInjectorCreator.build(InternalInjectorCreator.java:104)
        at com.google.inject.Guice.createInjector(Guice.java:96)
        at com.google.inject.Guice.createInjector(Guice.java:73)
        at hudson.ExtensionFinder$GuiceFinder.<init>(ExtensionFinder.java:281)
        at …

Note that neither the annotation nor the annotated member are shown in the stack trace; that seems similar to (but distinct from) an error better diagnosed in google/guice#1279.

Amends #16.