Remove set-mark-default-inactive?

[Chong Yidong]

The strange option `set-mark-default-inactive' was originally introduced
in a commit of completely unrelated stuff:

  revno: 93291
  committer: Stefan Monnier <address@hidden>
  timestamp: Sun 2008-12-21 05:20:06 +0000
  message:
  (completion-all-completions-with-base-size): Remove.
  (completion-all-completions): Don't set it.
  (completion-table-with-context, completion--file-name-table):
  Don't add base-size in last cdr.
  (completion-hilit-commonality): Add argument `base-size'.
  (display-completion-list, completion-emacs21-all-completions)
  (completion-emacs22-all-completions, completion-basic-all-completions):
  Provide it.
  (completion-pcm--all-completions): Don't need to remove the base-size
  in last-cdr any more.

Is this an accidental commit of a local experiment?  As far as I can
tell, setting `set-mark-default-inactive' to non-nil is pretty much the
same as disabling Transient Mark mode.  (See also Bug#10964.)

Should we simply delete this option?