Revert "cashew: use g_unix_signal_add to catch signals"

Reverting due to build failure on amd64 corei7 PFQ

This reverts commit 3e1c5e47407aa08de1795e4dc677c8bed2c864ad

Change-Id: I23382b2b64aa61c01e32f27bdd1330efda256d1b
Reviewed-on: https://gerrit.chromium.org/gerrit/13759
Commit-Ready: Josh Horwich <jhorwich@google.com>
Reviewed-by: Josh Horwich <jhorwich@google.com>
Tested-by: Josh Horwich <jhorwich@google.com>