Remove the free variable `vc-disable-async-diff`

Dependencies

• [2] CJQZS55X working annotation
• [3] ITWH4477 reindentation
• [4] MAGPFPZB init
• [5] SLZWA7AY another vc api fix

Change contents

• replacement in vc-darcs.el at line 470
  [3.16974]→[2.4224:4285](∅→∅)
  − (defun vc-darcs-diff (file &optional rev1 rev2 buffer dummy)
  [3.16974]

  [3.17035]
  + (defun vc-darcs-diff (file &optional rev1 rev2 buffer _async)
• replacement in vc-darcs.el at line 472
  [3.17101]→[3.17101:17197](∅→∅)
  − (let* ((async (not vc-disable-async-diff))

  − (rev1 (vc-darcs-rev-to-hash rev1 file t))
  [3.17101]

  [3.17197]
  + (let* ((rev1 (vc-darcs-rev-to-hash rev1 file t))
• replacement in vc-darcs.el at line 477
  [3.17452]→[3.17452:17730](∅→∅)
  − (let ((status (apply #'vc-do-command (or buffer "*vc-diff*")

  − (if async 'async 1)

  − vc-darcs-program-name file

  − "diff"

  − (append from to arguments))))

  − (if async 1 status))))
  [3.17452]

  [3.17730]
  + (apply #'vc-do-command (or buffer "*vc-diff*")

  + nil ;; https://debbugs.gnu.org/cgi/bugreport.cgi?bug=21969

  + vc-darcs-program-name file

  + "diff"

  + (append from to arguments))))