QtIFW

Set also display name for Repository action "remove"

We should use the display name parameter if given when using action:

<Repository action="remove" url="http://foo.bar" displayname="foobar"/>

I.e. when the repository gets removed it should print out the given
displayname. Now it always prints the url.

Change-Id: I227c02c45c21be3c7c93d57f4242e1fc5c189f3c
Reviewed-by: Samuli Piippo <samuli.piippo@qt.io>
Reviewed-by: Katja Marttila <katja.marttila@qt.io>