[ASTImporter] Remove duplicated and dead CXXNamedCastExpr handling code.

[teemperor]

Summary

CXXNamedCastExpr importing is already handled in the respective VisitCXXNamedCastExpr method.
So this code here can never be reached under normal circumstances and we might as well remove it.

This patch shouldn't change any observable behavior of the ASTImporter.

[teemperor]

See http://lab.llvm.org:8080/coverage/coverage-reports/clang/coverage/Users/buildslave/jenkins/workspace/clang-stage2-coverage-R/llvm/tools/clang/lib/AST/ASTImporter.cpp.html#L6044 for the test coverage entry.

lib/AST/ASTImporter.cpp

Expr *ASTNodeImporter::VisitExplicitCastExpr(ExplicitCastExpr *E) {
   case Stmt::ObjCBridgedCastExprClass: {
       auto *OCE = cast<ObjCBridgedCastExpr>(E);
       return new (Importer.getToContext()) ObjCBridgedCastExpr(
             Importer.Import(OCE->getLParenLoc()), OCE->getBridgeKind(),
             E->getCastKind(), Importer.Import(OCE->getBridgeKeywordLoc()),
             TInfo, SubExpr);
   }
   default:
-    break; // just fall through
-  }
-
-  auto *Named = cast<CXXNamedCastExpr>(E);
-  SourceLocation ExprLoc = Importer.Import(Named->getOperatorLoc()),
-      RParenLoc = Importer.Import(Named->getRParenLoc());
-  SourceRange Brackets = Importer.Import(Named->getAngleBrackets());
-
-  switch (E->getStmtClass()) {
-  case Stmt::CXXStaticCastExprClass:
-    return CXXStaticCastExpr::Create(Importer.getToContext(), T,
-                                     E->getValueKind(), E->getCastKind(),
-                                     SubExpr, &BasePath, TInfo,
-                                     ExprLoc, RParenLoc, Brackets);
-
-  case Stmt::CXXDynamicCastExprClass:
-    return CXXDynamicCastExpr::Create(Importer.getToContext(), T,
-                                      E->getValueKind(), E->getCastKind(),
-                                      SubExpr, &BasePath, TInfo,
-                                      ExprLoc, RParenLoc, Brackets);
-
-  case Stmt::CXXReinterpretCastExprClass:
-    return CXXReinterpretCastExpr::Create(Importer.getToContext(), T,
-                                          E->getValueKind(), E->getCastKind(),
-                                          SubExpr, &BasePath, TInfo,
-                                          ExprLoc, RParenLoc, Brackets);
-
-  case Stmt::CXXConstCastExprClass:
-    return CXXConstCastExpr::Create(Importer.getToContext(), T,
-                                    E->getValueKind(), SubExpr, TInfo, ExprLoc,
-                                    RParenLoc, Brackets);
-  default:
     llvm_unreachable("Cast expression of unsupported type!");
     return nullptr;
   }
 }
 
 Expr *ASTNodeImporter::VisitOffsetOfExpr(OffsetOfExpr *OE) {
   QualType T = Importer.Import(OE->getType());
   if (T.isNull())