Remove getName from ValueDecl

Push the getName method from ValueDecl down to only those types that are
guaranteed to have a name that is backed by an identifier and that will
not be special.

lib/Parse/Parser.cpp

@@ -770,7 +770,7 @@ void Parser::diagnoseRedefinition(ValueDecl *Prev, ValueDecl *New) {
   assert(New != Prev && "Cannot conflict with self");
   diagnose(New->getLoc(), diag::decl_redefinition, New->isDefinition());
   diagnose(Prev->getLoc(), diag::previous_decldef, Prev->isDefinition(),
-           Prev->getName());
+           Prev->getBaseName());
 }
 
 struct ParserUnit::Implementation {