Remove the rest of old-style copyright headers

src/catch2/internal/catch_singletons.cpp

@@ -1,10 +1,3 @@
-/*
- *  Created by Phil Nash on 15/6/2018.
- *
- *  Distributed under the Boost Software License, Version 1.0. (See accompanying
- *  file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
- */
-
 #include <catch2/internal/catch_singletons.hpp>
 
 #include <vector>