remove wrong version warner in extconf.rb

Author: Largo

ext/tk/extconf.rb

@@ -2096,5 +2096,4 @@ def pthread_check()
 else
   puts "\nCan't find proper Tcl/Tk libraries. So, can't make tcltklib.so which is required by Ruby/Tk."
   puts "If you have Tcl/Tk libraries on your environment, you may be able to use them with configure options (see ext/tk/README.tcltklib)."
-  puts "At present, Tcl/Tk8.6 is not supported. Although you can try to use Tcl/Tk8.6 with configure options, it will not work correctly. I recommend you to use Tcl/Tk8.5 or 8.4."
 end