remove override of site container max-width variable (css only) This makes the whole site slighly wider on wider screens.
remove override of site container max-width variable (css only)
This makes the whole site slighly wider on wider screens.

Removing this override as it isn't necessary and makes our theme
more complex.

relates to #503

openaustralia/righttoknow,openaustralia/righttoknow,openaustralia/righttoknow