base/smartptr.h: Get rid of m_ptrStr member

Every ePtr<> gets an extra char[9] added for no other reason than to
implement an obscure getPtrString() function which isn't being used
anywhere, except in ServiceEventTracker.py which doesn't care about
the type of object returned.

Just implement the method as returning an intptr, which serves the
same purpose, but doesn't need any local storage.