Bug 969193 - ][Cost Control] The string "OK" is not localizable when launching cost control with a locked SIM

Button is using a non existent string ID. Existing string with id “ok”
seems to be unused in other contexts.
Merge pull request #16084 from flodolo/bug969193_okcostcontrol

Bug 969193 - [Cost Control] The string "Ok" is not localizable when launching cost control with a locked SIM