It appears to be a quote from an email that existed before the climategate emails:
http://strongasanoxandnearlyassmart.blogspot.com/2007/02/we-have-to-get-rid-of-medieval-warm.html
“We have to get rid of the Medieval Warm Period,” David Deming, a geoscientist at the University of Oklahoma, was e-mailed by a major participant in the IPCC assessments. As Dr. Lindzen confirmed, this was accomplished by the Third Assessment in 2001.
http://www.epw.senate.gov/hearing_statements.cfm?id=266543
Yes, it’s in this Senate hearing as an unattributed email.
But it’s not in the whistleblower set of emails.
No doubt that they eliminated MWP, it’s in the open literature. Or it WAS, and the new releases don’t have it.