[ODRHash] Do not rely on Type* when computing the hash.

ODRHash aims to provide Cross-TU stable hashing. Making clang::Type pointer
part of the hash connects (remotely) the ODRHash with the TU-specific
::Profile hasher.

r332281 exposed the issue by changing the way the ASTContext different
elaborated types if there is an owning tag. In that case, ODRHash stores two
 different types in its TypeMap which yields false ODR violation in modules.

The current state of implementation shouldn't need the TypeMap concept
anymore. Rip it out.

Differential Revision: https://reviews.llvm.org/D48524

llvm-svn: 335853