DOC: Remove tooltip non-functional suggestion

The tooltip previously gave an example of using 'randint(5)' as an argument to the row selection field in the loop dialog. This would actually lead to an error:
TypeError: range() integer end argument expected, got numpy.float64.
numpy.randint() does return an integer so not sure why this error arises, but removing the suggestion from the tooltip in the interim.
Merge pull request #662 from m-macaskill/patch-2

DOC: Remove tooltip non-functional suggestion