Remove Linter#message

We don't want to use this method of defining a default lint message, as
it's a little silly to define a public method that only gets used
internally.

Convert the only use of this method to a CONSTANT definition.

Change-Id: Iad625eb0564bce7d0f56c7ae0b8ce72ef4f03ae7
Reviewed-on: http://gerrit.causes.com/42560
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Shane da Silva <shane.dasilva@brigade.com>