shill: cellular: Delete CellularOperatorInfo.

|CellularOperatorInfo| has been replaced by |MobileOperatorInfo|. Unwire the few
remaining places, and delete the old object.

BUG=chromium:371639
TEST=(1) Run shill_unittest
     (2) Run network_3GSmokeTest on a few modems.

Change-Id: Ib840f10c034f9777a504c0fb04eb442cdcb0ffb0
Reviewed-on: https://chromium-review.googlesource.com/201101
Reviewed-by: Thieu Le <thieule@chromium.org>
Commit-Queue: Prathmesh Prabhu <pprabhu@chromium.org>
Tested-by: Prathmesh Prabhu <pprabhu@chromium.org>