[lldb] Replace radar link with documenting comment (NFC)

This replaces the radar link with a comment explaining the underlying
problem, which is that when the (dynamic) type of an object changes, so
does their synthetic filter of choice, which requires us to regenerate
the filter.

Author: JDevlieghere

lldb/source/Core/ValueObjectSyntheticFilter.cpp

@@ -163,8 +163,8 @@ bool ValueObjectSynthetic::UpdateValue() {
     return false;
   }
 
-  // regenerate the synthetic filter if our typename changes
-  // <rdar://problem/12424824>
+  // Regenerate the synthetic filter if our typename changes. When the (dynamic)
+  // type of an object changes, so does their synthetic filter of choice.
   ConstString new_parent_type_name = m_parent->GetTypeName();
   if (new_parent_type_name != m_parent_type_name) {
     LLDB_LOGF(log,