Release notes about cloud image updates are removed because they refer
to unsupported systems.

Change-Id: I020ca65b2ec1d4be4f6660f9b90be80e952138b0

This is continue of the changes to support Ironic/Bifrost provision
through DHCP-relay same as I9488a72db588e31289907668f1997596a8ccdec6

Depends-On: I74af38dc555b7edee8331e31dfd1a2fbfe4f1151
Change-Id: Ie1d5ecf32c637b77757e56fbe2fae1ff7c0bf000
Signed-off-by: Maksim Malchuk <maksim.malchuk@gmail.com>