doc: remove upgrade instructions for earlier releases
doc: remove upgrade instructions for earlier releases

As we have deprecated earlier versions than v3.3.0, it is not required
to keep the upgrade docs for the same. The upgrade doc for v3.2.0 to
v3.3.0 has been kept intact.

Signed-off-by: Humble Chirammal <dc8ba7e82a7df22725dedec9b10c7aaab9ec713f@redhat.com>

ceph/ceph-csi,ceph/ceph-csi,ceph/ceph-csi,ceph/ceph-csi