Revert " Bug 966729 - Fix typo to really disable test_privileged_app_contacts_prompt test"

This reverts commit 53483b08ac780d19c085874006763bb1ef45c83d.
Revert "Bug 966729 - Disable test_privileged_app_contacts_prompt test until new b2g build r=me"

This reverts commit 8b0e09bb13c3f7827ce8093ce969dca754414573.
Merge pull request #15911 from zacc/bug_966729

Bug 966729 - Revert disable test_privileged_app_contacts_prompt.py