SDL_test: remove unused BuildCommonUsageString

include/SDL3/SDL_test_common.h

@@ -170,19 +170,6 @@ int SDLTest_CommonArg(SDLTest_CommonState *state, int index);
  */
 void SDLTest_CommonLogUsage(SDLTest_CommonState *state, const char *argv0, const char **options);
 
-/**
- * \brief Returns common usage information
- *
- * You should (probably) be using SDLTest_CommonLogUsage() instead, but this
- *  function remains for binary compatibility. Strings returned from this
- *  function are valid until SDLTest_CommonQuit() is called, in which case
- *  those strings' memory is freed and can no longer be used.
- *
- * \param state The common state describing the test window to create.
- * \returns a string with usage information
- */
-const char *SDLTest_CommonUsage(SDLTest_CommonState *state);
-
 /**
  * \brief Open test window.
  *