Fix reset for y-grid to clear max-width as well

[kball]

Fixes issue where grid-y cells are still constrained by the width set by grid-x cells.

Fixes

To

[rafibomb]

I see the docs does that but not in a 6.4.3 codepen https://codepen.io/rafibomb/pen/yzgXZm
In the CSS it looks like width is reset properly

[kball]

Digging into this further, the situation occurs when you have both the xy grid and the traditional flex-grid in the page. The XY grid is much more careful about specificity than the traditional grid... that said, this is intended to be a supported case, so i'd like the reset to work.

[rafibomb]

That's what it is - makes sense!