nvdaHelper SCons files:
*No longer use an sconscript file to generate the vbuf RPC stubs. Instead let each component that needs the stubs generate them themselves with the MSRPCStubs builder.
*All components that generate vbuf or nvdaController RPC stubs now make use of the new MSRPCStubs construction variables to configure the method name prefix, or to disable the creation of server stubs or client stubs if they are not needed. E.g. Local can disable server stubs for vbuf as it does not need them.
