Remove workaround for ROOT/cling problem with Boost small_vector

To be used for creating a reproducer and testing upcoming ROOT builds.

closes #75

Kernel/LHCbKernel/Kernel/MonotonicArena.h

@@ -66,15 +66,8 @@ namespace LHCb::Arena {
     /// One byte past the end of the current block, or nullptr if it doesn't exist.
     std::byte* m_current_end{nullptr};
 
-    // Explicitly specify boost::container::small_vector default template arguments
-    // to sidestep cling error, see lhcb/LHCb#75
-#if BOOST_VERSION < 107100
     /// All memory blocks owned by this arena.
-    boost::container::small_vector<gsl::span<std::byte>, 1, void> m_all_blocks;
-#else
-    /// All memory blocks owned by this arena.
-    boost::container::small_vector<gsl::span<std::byte>, 1, void, void> m_all_blocks;
-#endif
+    boost::container::small_vector<gsl::span<std::byte>, 1> m_all_blocks;
 
     /// Approximate factor by which each block is larger than its predecessor.
     static constexpr std::size_t growth_factor = 2;