Rename colorful user gallery avatar

Summary: In D20536 we rename the colorful user avatar to `user-man`. This patch changes that avatar to the name "Man" to match the new name.

Test Plan: Open the avatar gallery.

Reviewers: #plasma, #vdg, ngraham, afiestas, broulik, davidedmundson

Reviewed By: #plasma, #vdg, ngraham, davidedmundson

Subscribers: davidedmundson, ngraham, #vdg, plasma-devel, #plasma

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D20564