addRestrictions was taking a branch parameter, binding its logic
to that of addBranchRestrictions. Since we will need to use it
for updating the facts table for induction variables, refactor it
to remove the branch parameter.

Passes toolstash -cmp.

Change-Id: Iaaec350a8becd1919d03d8574ffd1bbbd906d068
Reviewed-on: https://go-review.googlesource.com/104036
Run-TryBot: Giovanni Bajo <rasky@develer.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>