Columns Block: Investigate removing Newspack-specific styles

[laurelfulford]

Early on, we added some Columns styles to the Newspack Blocks plugin, to override how the columns wrapped in Gutenberg's default styles.

These styles have caused issues since then -- both when the Columns block was updated in WP 5.9, and when they clash with plugins (like the Publisher Media Kit plugin).

We should test and see if we can remove these styles at this point -- if we can, it could make things easier to maintain down the road.

[laurelfulford]

Closed with #1133.