Remove deprecated parameters

* horizon::swift (deprecated since 2.1.0)
* horizon::keystone_scheme (deprecated since 4.0.0)
* horizon::keystone_host (deprecated since 4.0.0)
* horizon::keystone_port (deprecated since 4.0.0)
* horizon::can_set_mount_point (deprecated since 4.0.0)

Change-Id: I1675511b5733434e65a2958fd5c18844a3b42ff9