meta-phosphor: drop ipmi-channel-config

phosphor-host-ipmid no longer does anything with the information
specified by the ipmi-channel-config, therefore drop it.

(From meta-phosphor rev: 14e259d7b53de1bae200ee5c5dbf201ffd105543)

Change-Id: I74057fd68ba7e46e5cf5850eaf6434cb6bb37ec9
Signed-off-by: Patrick Venture <venture@google.com>
Signed-off-by: Andrew Geissler <geissonator@yahoo.com>