Fix sideways scrolling on service priority organisation pages #2194
Outcome is a page that looks exactly the same but doesn’t sideways scroll.
Example of live bug: https://www.gov.uk/government/organisations/driver-and-vehicle-standards-agency
The `.service-priority` class was including grid-row styles to contain floats, but this came with a large negative margin. This negative margin caused sideways scrolling on thin page widths. Instead use the existing `floated-children` class on the inner block to contain the floats (and alter padding at different screen sizes) and stop extending with `grid-row`. Outcome is a page that looks exactly the same but doesn’t sideways scroll.