[web] Use of inexistent property use_libspotity

[hacketiwack]

Current situation

A warning is thrown in the console of the web browser informing that the property use_libspotity is not defined.
Consequently, a message regarding the authentication to Spotify is hidden.

Expected situation

The warning is not shown in the console.

Steps to reproduce the issue

1. In the web interface, go to the settings and go in the "Online Services" tab.
2. The console gives an warning that the property use_libspotity is not defined. (Note the spelling mistake.)

Comment

The property use_libspotify seems to have disappeared, or never existed.

Version

Latest

Platform

All

[hacketiwack]

The fix corrects the issue.