Notifications - Remove "Completed Challenges" until Backend is ready

[luizrrodrigues]

• Remove Completed Challenges tab from listing page
• Change Active Challenges tab to just Challenges
• The Challenges tab will show both Active and Completed challenges notifications for now

[SathyaJayabal]

verified on test env

[SathyaJayabal]

verified on beta(feature branch)

[SathyaJayabal]

verified on beta. (develop branch)