Bug 1022644 - [Messages] Can't open the recipient panel if there are only 2 lines of recipients

- Remove unnecessary property dims and replace it with minheight element style
ya, I think it's reasonable. I'll only left the display and align-items(since it could only work with flex, put it in the original won't break anything, it just looks weird for me) in ```section[role="region"].new #messages-to-field```. @azasypkin  wdyh?