Don't show the info icon on the big preview delegate

Summary:
As discussed on the VDG chat with the original author of the design,
the information icon was supposed to be an interactive component,
but as the functionality is covered already, it adds nothing new
and as such we do not need it (and it might in fact be considered
confusing, since it looks like it is special when in fact it is not).

BUG:413436

Test Plan:
Before:

After:

Reviewers: Frameworks, KNewStuff, ngraham, abetts, VDG, ndavis

Reviewed By: VDG, ndavis

Subscribers: kde-frameworks-devel

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D25855