Remove warning prompt when viewing a post from message list, Fixes T652

Summary:
  - Remove event `viewPost`
  - Remove call to `viewPost` function

Test Plan:
 - Click on `View Post` link from message list
 - See page load without an alert prompt

Reviewers: rjmackay, shadowhand

Reviewed By: shadowhand

Subscribers: srutto, lkamau

Maniphest Tasks: T652

Differential Revision: https://phabricator.ushahidi.com/D292