Delete redundant and monochrome versions of applications-internet
applications-internet is the only category icon that has monochrome versions at small
sizes. In addition, there's a copy of it (same name and appearance) in preferences.
This patch corrects those two issues by deleting the monochrome and redundant versions.
Only the colorful version shows up in Cuttlefish:
With the patch to add icons to Discover's sidebar (D22716), all icons are now colorful:
Reviewers: VDG, ndavis
Reviewed By: VDG, ndavis
Differential Revision: https://phabricator.kde.org/D22733