Bug 883090 - [Sounds] Remove startup shutdown sounds

[\#883090](https://bugzilla.mozilla.org/show_bug.cgi?id=883090) Revert:

[\#879869](https://bugzilla.mozilla.org/show_bug.cgi?id=879869) - Disable startup/shutdown sound by default
[\#801895](https://bugzilla.mozilla.org/show_bug.cgi?id=801895) - Sounds Update Boot Sounds
[\#812245](https://bugzilla.mozilla.org/show_bug.cgi?id=812245) - [Sound] Shut Down Animation Needs a sound
[\#877813](https://bugzilla.mozilla.org/show_bug.cgi?id=877813) - [Sounds] Control to turn off Boot and Shutdown Sounds is needed in Settings