Revert "Bug 973156 - [Music] Send mozinterruptbegin and mozinterruptend to media playback widget for displaying the correct play status"

This reverts commit 0682e21ae9c7406828ad013c9238e4aa1fe84fe1.
Merge pull request #16871 from dominickuo/revert-bug-973156

Revert "Bug 973156 - [Music] Send mozinterruptbegin and mozinterruptend to media playback widget for displaying the correct play status"