deps: update fmt to latest version (#3403)

This updates `fmt` to the latest version and moves to just being a copy
of their repo to make updating easier (no editing their cmake / figuring
out which files to minimally include).

The motivation for this is now that we switched to C++ 20, there were a
ton of deprecated function usages that is going away in future compiler
versions. This gets rid of all those warnings.

game/kernel/common/klink.cpp

@@ -6,7 +6,7 @@
 #include "game/kernel/common/fileio.h"
 #include "game/kernel/common/kscheme.h"
 
-#include "third-party/fmt/core.h"
+#include "fmt/core.h"
 
 namespace {
 // turn on printf's for debugging linking issues.
@@ -260,4 +260,4 @@ Ptr<u8> c_symlink2(Ptr<u8> objData, Ptr<u8> linkObj, Ptr<u8> relocTable) {
   } while (*relocPtr);
 
   return make_ptr(relocPtr + 1);
-}
+}