fix compiler warnings:

 warning C4584: 'Ime::TextService' : base-class 'ITfTextInputProcessor' is already a base-class of 'ITfTextInputProcessorEx'
 warning C4584: 'Ime::CandidateListUIElement' : base-class 'ITfUIElement' is already a base-class of 'ITfCandidateListUIElement'
 warning C4101: 'candidateSize' : unreferenced local variable