x11/xscreensaver: remove XFT option

Xft isn't optional: it is mandatory, and xscreensaver configure
complains if it isn't there (but completes with a successful
exit code, which is a bit strange). Without XFT, the build
eventually fails like so:

dialog.c:695:52: error: use of undeclared identifier 'FcChar32'

if (XftCharExists (ws->dpy, ws->label_font, (FcChar32) *uc))

PR: 263869
Reported by: riggs
Approved by: build-fix blanket