Find{TCL,Tclsh,TclStub}: Remove matches for non-existent Tcl/Tk 8.7

Version 8.7 of Tcl/Tk never made it past alpha status.
What was briefly labeled 8.7a5 eventually released as 9.0.0.

And in FindTclStub, also remove patterns for ttkstub8.8, which
even more than 8.7 never actually existed.