[rootcling] Remove check for unique_ptr members

Since llvm/llvm-project@f5e687d
libc++ implements _LIBCPP_COMPRESSED_PAIR with an anonymous struct (a
Clang extension). This results in unique_ptr having a single FieldDecl
with an empty name that does not appear as a data member in TClass.
Instead, the AST has multiple IndirectFieldDecl's that "refer" into
the anonymous struct.

In ROOT, we now have two options: We could support anonymous structs,
either by allowing data members with empty names or by adding all
indirect field declarations as members. However, I would argue that
we actually do NOT want to support this extension for IO classes.
Instead remove the (questionable) check in rootcling that verifies
the number of data members in unique_ptr.

(cherry picked from commit fff03d2)

Author: hahnjo

io/rootpcm/src/rootclingIO.cxx

@@ -78,26 +78,6 @@ static bool IsUnsupportedUniquePointer(const char *normName, TDataMember *dm)
 
       if (!isUniquePtrOffsetZero) return true;
 
-      auto clm = TClass::GetClass(dmTypeName);
-      if (!clm) {
-         Error("CloseStreamerInfoROOTFile", "Class %s is not available.", dmTypeName);
-         return true;
-      }
-
-      // TODO: Is it not clear what situation we are checking for by checking if
-      // the unique_ptr class has any data members.
-      clm->BuildRealData(nullptr, /* istransient = */ true);
-      auto upDms = clm->GetListOfRealData();
-      if (!upDms) {
-         Error("CloseStreamerInfoROOTFile", "Cannot determine unique pointer %s data members.", dmTypeName);
-         return true;
-      }
-
-      if (0 == upDms->GetSize()) {
-         Error("CloseStreamerInfoROOTFile", "Unique pointer %s has zero data members.", dmTypeName);
-         return true;
-      }
-
       // We check if the unique_ptr has a default deleter
       std::vector<std::string> out;
       int i;