[applets/kickoff] Remove "Switch tabs on hover" option

This option confuses people into believing that it applies to the
category sidebar, but it does not: it only applies to the tabs below or
above it (strike 1). It is off by default (strike two), and if you turn
it on, it worsens usability by making it easier to accidentally switch
tabs while moving the mouse over to an app you want to click on (strike
3). There is no conceivable use case that is improved by turning it on.

3 strikes and you're out, so let's remove this option. :)