This PR excludes the Tcl/Tk libraries from the included Tahoe-LAFS binary bundle (which are needlessly included by PyInstaller) on Windows, reducing the total filesize of the application on-disk by about 10 MB. Note that Tcl/Tk is already excluded for macOS and Linux binary distributions; this PR merely updates the Windows build script to use the same/correct PyInstaller ".spec" file (which, apparently, I forgot to do earlier).