There were some unwraps here that we can get rid of if we unduplicate
the work Message::read already does. That goes in Message::read_with_detailed_error.
Delete a fuzz corpus file that was actually wrong, but allowed by Message::read's
previous lax semantics.
Make it clear that the name passed into ClientSession is a DNS name
and cannot be empty (""), an IP address, an internationalized domain
name, etc. It has to be a DNS hostname because it is put into the SNI
extension in the client hello.