CLC-3551 /api/blog should update the alert field every 2 minutes

Removed the following line from the BlogFeedController:

 - caches_action(:get_latest_release_notes, :expires_in => EtsBlog::ReleaseNotes.expires_in)

EtsBlog::ReleaseNotes::get_latest_release_notes is already being cached with the default expiration time.
Merge pull request #2337 from chikoon/CLC-3551-2-minute-cache-expiration-for-api-blog-alerts

CLC-3551 /api/blog should update the alert field every 2 minutes