The Migration Assistance API has been functionally replaced by the
Deprecation Info API, and the Migration Upgrade API is not used for the
transition from ES 6.x to 7.x, and does not need to be kept around to
repair indices that were not properly upgraded before upgrading the
cluster, as was the case in 6.
This commit gets rid of the 'NONE' and 'INFO' severity levels for
deprecation issues.
'NONE' is unused and does not make much sense as a severity level.
'INFO' can be separated into two categories: Either 1) we can
definitively tell there will be a problem with the cluster/node/index
configuration that can be resolved prior to upgrade, in which case
the issue should be a WARNING, or 2) we can't, because any issues would
be at the application level, for which the user should review the
deprecation logs and/or response headers.
Gordon Brown
Lisa Cawley
Benjamin Trent
Przemyslaw Gomulka