Fix some trivial cppcheck warnings
Fix cppcheck complaint for lex.yy.c: style: struct member 'yy_trans_info::yy_verify' is never used. style: struct member 'yy_trans_info::yy_nxt' is never used.
The vtkXRenderWindowTclInteractor class had an "Internal" member variable that shadowed the "Internal" member of its superclass, I renamed the former to "TclInternal".
The cppcheck warning for vtkPixelExtent seems to be spurious, but the fix should (hopefully) silence it: Member variable 'vtkPixelExtent::Data' is not assigned a value in assignment operator.