Remove unused enum values.

Which means that these methods simplify to constant values:
   ItemConnectionBase::GetEnableState() -> TRISTATE_INDET
   ItemConnectionBase::IsActive() -> true
so inline those values.

Which means that ControlWrapperBase::ModifyControl is always called with
a first parameter of TRISTATE_INDET, so drop that first parameter.

Change-Id: I6d63b63b2f15faad2336665f60e7239e35b74e47