Remove redundant passing around of a "ContainsAutoType" flag.

Remove redundant passing around of a "ContainsAutoType" flag.

This flag serves no purpose other than to prevent us walking through a type to
check whether it contains an 'auto' specifier; this duplication of information
is error-prone, does not appear to provide any performance benefit, and will
become less practical once we support C++1z deduced class template types and
eventually constrained types from the Concepts TS.

No functionality change intended.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@291737 91177308-0d34-0410-b5e6-96231b3b80d8