gnu: gnome-vfs: Expect 'test-async-cancel' failure, and clean up.

* gnu/packages/gnome.scm (gnome-vfs)[arguments]: Add
  "XFAIL_TESTS=test-async-cancel" to make flags.  Remove ignored and
  undocumented 'DISABLE_DEPRECATED_CFLAGS' configure flag.  Simplify
  'ignore-deprecations' phase and return #t.  Reformat to fit within
  80 columns.