Simplify some C++ abstractions (#1518)

* Remove namespaces
* Prefer `bool operator==`, not `friend auto operator==`
* Prefer not to use `using`
* Use a `constexpr` function instead of a template for `flipTable`

include/gfx/pal_packing.hpp

@@ -6,19 +6,15 @@
 #include <tuple>
 #include <vector>
 
-#include "defaultinitalloc.hpp"
+#include "defaultinitvec.hpp"
 
 struct Palette;
 class ProtoPalette;
 
-namespace packing {
-
 /*
  * Returns which palette each proto-palette maps to, and how many palettes are necessary
  */
 std::tuple<DefaultInitVec<size_t>, size_t>
     overloadAndRemove(std::vector<ProtoPalette> const &protoPalettes);
 
-} // namespace packing
-
 #endif // RGBDS_GFX_PAL_PACKING_HPP