reports: do not provide default theme

This can cause upgrade issue from version to version in JRS.

Change-Id: I82023e99e8efe402df41e80d52bc33ac012e80f7
Bug-Url: https://bugzilla.redhat.com/1112641
Signed-off-by: Yaniv Dary <ydary@redhat.com>
(cherry picked from commit 2265cc8eea7e1369b941eec2b1e4d566be5ac360)