lib: stop overriding system printf symbols

After this patch, the codebase no longer overrides system printf
functions. Instead it explicitly calls either the curl printf functions
`curl_m*printf()` or the system ones using their original names.

Also:
- drop unused `curl_printf.h` includes.
- checksrc: ban system printf functions, allow where necessary.

Follow-up to db98daab05 #18844
Follow-up to 4deea9396b #18814

Closes #18866

lib/hostip.c

@@ -64,8 +64,7 @@
 #include "easy_lock.h"
 #include "curlx/strparse.h"
 
-/* The last 3 #include files should be in this order */
-#include "curl_printf.h"
+/* The last 2 #include files should be in this order */
 #include "curl_memory.h"
 #include "memdebug.h"
 
@@ -176,7 +175,7 @@ create_dnscache_id(const char *name,
     len = buflen - 7;
   /* store and lower case the name */
   Curl_strntolower(ptr, name, len);
-  return msnprintf(&ptr[len], 7, ":%u", port) + len;
+  return curl_msnprintf(&ptr[len], 7, ":%u", port) + len;
 }
 
 struct dnscache_prune_data {