STYLE: revert bitSet/HashSet setMany() to set() method (issue #837)

- improves backward compatibility and more naming consistency.
  Retain setMany(iter1, iter2) to avoid ambiguity with the
  PackedList::set(index, value) method.

src/fileFormats/ensight/file/ensightCase.C

@@ -109,7 +109,7 @@ Foam::label Foam::ensightCase::checkTimeset(const labelHashSet& lookup) const
         }
 
         // OR
-        // tsTimes.unsetMany(timesUsed_.toc());
+        // tsTimes.unset(timesUsed_.toc());
 
         if (tsTimes.empty())
         {