You are looking for an 'x' like in the upper right corner of a Windows window, to close a window?
AFAIK, that's not supported out of the box. IMHO, something like you are already using and suggested by Sunny is the recommended way to achieve what the user wants, being able to remove and add columns, right?
BTW, how does the user wants to add a column again after he has removed it?
I would suggest that you train the user about the way QlikView is designed to work.
If he insists and pay you a lot of money for the feature, you could try
- creating an extension that shows this specific feature
- fiddling around with some text objects 'x' as overlay on your chart, an action could be created to hide the columns conditionally. But since you are changing the chart layout each time you are removing a column, this will get really messy