Revert "[clang] Don't inherit dllimport/dllexport to exclude_from_explicit_instantiation members during explicit instantiation (#65961)"

This uncovered a problem with virtual methods and
exclude_from_explicit_instantiation, see
#66909

Reverting until that's fixed.

> This is a continuation of https://reviews.llvm.org/D155713
>
> Fixes #40363

This reverts commit 84216d1.

Author: zmodem

clang/lib/Sema/SemaDeclCXX.cpp

@@ -6605,13 +6605,6 @@ void Sema::checkClassLevelDLLAttribute(CXXRecordDecl *Class) {
     if (!VD && !MD)
       continue;
 
-    if ((TSK == TSK_ExplicitInstantiationDeclaration ||
-         TSK == TSK_ExplicitInstantiationDefinition) &&
-        Member->hasAttr<ExcludeFromExplicitInstantiationAttr>()) {
-      // Skip members excluded from instantiation.
-      continue;
-    }
-
     if (MD) {
       // Don't process deleted methods.
       if (MD->isDeleted())