Add Delete Parameter option before selecting a parameter

[leohsiang]

Description

Consider adding the Remove Parameter button in this spot before selecting a parameter: https://www.screencast.com/t/2Nfa3qxt

Steps for testing

References:

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[tomusborne]

There isn't really anything to delete yet as nothing has been added. For example, doing nothing and refreshing the page will simply remove the dropdown. Will keep an eye on this to see if more people are confused by it.