SDL_syswm.h: removed SDL_SYSWM_MIR

include/SDL_syswm.h

@@ -137,7 +137,6 @@ typedef enum
     SDL_SYSWM_COCOA,
     SDL_SYSWM_UIKIT,
     SDL_SYSWM_WAYLAND,
-    SDL_SYSWM_MIR,  /* no longer available, left for API/ABI compatibility. Remove in 2.1! */
     SDL_SYSWM_WINRT,
     SDL_SYSWM_ANDROID,
     SDL_SYSWM_VIVANTE,