Add homeassistant.remove_area_from_floor service

Description

SSIA, adds a service to remove an area from a floor. Since an area can only be in a single floor at a time, there is no need to ask for floor input. This service simply clear the floor from the selected area.

Motivation and Context

How has this been tested?

Screenshots (if appropriate):

Types of changes

[ ] Bug fix (non-breaking change which fixes an issue)
[x] New feature (non-breaking change which adds functionality)
[ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
[ ] Other

Checklist

[x] My code follows the code style of this project.
[x] My change requires a change to the documentation.
[ ] I have updated the documentation accordingly.

frenck / spook

Add homeassistant.remove_area_from_floor service #707