frontend: minor instance type correction

Previously when changing display type on entity, InstanceTypeManager
prevented the change to happen.

This patch removes deactivating and activating instance type manager
when display type of entity changes which caused this problem.

Change-Id: I85f2301e12b194c8373d7f531e077e52d49b9d02
Signed-off-by: Frantisek Kobzik <fkobzik@redhat.com>