sounds like a job for jira. add a jira to kill the provider, tag that jira in the commit. Then either via jira or git log, it is clear when it happened and the single commit that could possibly be reverted.
+1 for using JIRA to record the details. I don't know how well searchable JIRA is, though - it would be nice if someone searching for "jclouds <attic-provider-name>" in a search engine would be able to find a link to that commit...
ap
