applets/weather: Fix spacing on forecast view

Remove a now unncessary size hint, which was artificially increasing the minimum icon separation in the forecast view, allowing for a more compact view.

This was specially wrong for the Environment Canada provider, where we hide the "night" labels, but were taking their width into account.

It is a standalone bugfix but should also help with !522 (comment 851707)

	BEFORE	AFTER
Free-form minimum size
Constrained in system tray