Removes dependency on hardening-wrapper

This commit bumps compat level to 9, allowing for
DEB_BUILD_MAINT_OPTIONS to be used to specify that
hardening is desired, allowing for dpkg-buildflags
to intelligently set the hardening options passed
to gcc etc. (closes: Debian#836762).

Signed-off-by: Peter Palfrader <peter@palfrader.org>