Revert "bootstrap: make sure slingshot bootstrap overrides correctly."

This reverts commit ee7a39d8cd918549c69c161232186b6bd254ca06.
* build-aux/bootstrap.slingshot: Due to multiple section recurrences
in upstream bootstrap.in, this didn't work anyway.
* bootstrap: Regenerate.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>