Revert "Stop playback of media files when leaving page."

Causes *all* audio playback to pause, not just from the
app. 

See https://ticket.wikimedia.org/otrs/index.pl?Action=AgentZoom&TicketID=7613380

This reverts commit 4b7bc667442c9f2d619873c89497efd098894785.

Change-Id: Ia200bf6f5ce49dce695a9f19a258badde7b65589
Merge "Revert "Stop playback of media files when leaving page.""