Revert "Revert "Add hidserv-stats filname to our sandbox filter""

This reverts commit 5446cb8d.

The underlying revert was done in 0.2.6, since we aren't backporting
seccomp2 loosening fixes to 0.2.6.  But the fix (for 17354) already
went out in 0.2.7.4-rc, so we shouldn't revert it in 0.2.7.