Similarly to dab5457620 "Fix deleting FrameManagerImpl*", we need a
virtual destructor. clang was complaining about it:

src/speechPlayer/src/speechPlayer.cpp:52:2: warning: delete called on 'SpeechWaveGenerator' that is abstract but has non-virtual destructor [-Wdelete-abstract-non-virtual-dtor]
        delete playerHandleInfo->waveGenerator;
        ^

delete playerHandleInfo->frameManager wasn't actually calling
FrameManagerImpl~, because playerHandleInfo->frameManager is only a
FrameManager, which didn't have a destructor, and nothing was saying that
it's actually a FrameManagerImpl behind. Adding a virtual destructor
fixes that.