Update all sources from freedesktop.org to use https

* gnu/packages/xorg.scm:
* gnu/packages/xdisorg.scm:
* gnu/packages/video.scm:
* gnu/packages/tls.scm:
* gnu/packages/python.scm:
* gnu/packages/pulseaudio.scm:
* gnu/packages/polkit.scm:
* gnu/packages/pdf.scm:
* gnu/packages/libcanberra.scm:
* gnu/packages/gtk.scm:
* gnu/packages/gstreamer.scm:
* gnu/packages/gnome.scm:
* gnu/packages/glib.scm:
* gnu/packages/ghostscript.scm:
* gnu/packages/freedesktop.scm:
* gnu/packages/fontutils.scm: Update all sources hosted on freedesktop
  to fetch tarballs via https.  freedesktop.org appears to have updated
  recently to redirect all http to https.  As an exception, we leave
  pkg-config like it is, because pkg-config is needed to build gnutls,
  and without gnutls we can't download https URLs.