vdl/java: change VdlOptional<T extends VdlValue> to VdlOptional<T>
vdl/java: change VdlOptional<T extends VdlValue> to VdlOptional<T>

Change-Id: I5602f52af35e46775f70e36091197d1b7e098b84

vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref