bug#24946: 26.0.50; semantic/util-modes.el uses deprecated (and removed in git repo) symbol

[Glenn Morris]

Vladimir Lomov wrote:

> as topic states, cedet/semantic/util-modes.el uses symbol
> 'default-header-line-format' (it checks if this symbol is bound by means
> of 'boundp') but this symbol was removed in commit '73d47d22197'
> (http://git.savannah.gnu.org/cgit/emacs.git/commit/lisp?id=73d47d22197175f08b2dd62e76d7138872e611d2).

Picking at random from items deleted in that commit, one quickly finds
other problems, eg

emacs -Q -l feedmail
   -> Symbol's value as variable is void: default-fill-column

Every item deleted should have been checked for usage.