Clear the lines of a tooltip, both left and right.
- If this method is called when the GameTooltip is visible it will clear all the text but won't hide it
- The text isn't actually cleared, merely hidden. After a call to this method, the text can still be retrieved using FontString:GetText() on the GameTooltip's FontString children.
- The owner of the GameTooltip is cleared. i.e. calling GameTooltip:GetOwner() after calling this method will return nil.