Bug 11431: (QA followup) Typo in help file / variable name

Bug 11431: (QA followup) Typo in help file / variable name

Fixes the variable name to avoid a double-up that made it
impossible to turn off the sounds in general. If AudioAlerts
are turned off, they will only work on the audio administration
page now so you can set up and test the different sounds there.

Also fixes a little typo in the help file.

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>