Remove obsolete SVN $Id$ tags from source files

Remove SVN $Id$ tags from source files which have been made
obsolete by moving to git and serve no purpose any more.

This mostly removes the matches printed by the command

    git grep -E '\$[A-Za-z]+\$'

The remaining exceptions are some binary files (PDF and font files),
and jquery js files with both $Id$ and $Date$ tags.

src/usbdevs.h

@@ -16,8 +16,6 @@
  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  */
 
-/* $Id$ */
-
 /*
  * defines for the USB interface
  */