Remove a bunch of cruft and dead code for handling the case when types were

defined in function constant pools.  The assembler grammar has long
disallowed functions from having constant pools, so all of this stuff is
dead.

This makes it an immediate error for functions to refer to nonexisting
types, fixing Regression/Verifier/2005-03-21-UndefinedTypeReference.ll.

Before, references to non-existing types in functions would only be
detected when the subsequent function was parsed, due to the call to
"ResolveTypes".  "ResolveTypes" has not resolved any types for a long time,
instead it emitted an error message if no resolved types are left.  Since
the only caller of this method is in the module code, just inline it.

llvm-svn: 20726