Remove the rest of old-style copyright headers

src/catch2/internal/catch_main.cpp

@@ -1,8 +1,3 @@
-/*
- *  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/catch_session.hpp>
 #include <catch2/internal/catch_compiler_capabilities.hpp>
 #include <catch2/internal/catch_leak_detector.hpp>