dim: Squelch the filter-branch warning and wait

We actually want to use git filter-branch, so make it shut
up and do what it's told.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
3 jobs for master in 27 seconds (queued for 1 second)