[mir] Point to SDL_EGL_UnloadLibrary vs doing it our selfs

src/video/mir/SDL_miropengl.c

@@ -73,12 +73,6 @@ MIR_GL_LoadLibrary(_THIS, const char* path)
     return 0;
 }
 
-void
-MIR_GL_UnloadLibrary(_THIS)
-{
-    SDL_EGL_UnloadLibrary(_this);
-}
-
 void*
 MIR_GL_GetProcAddress(_THIS, const char* proc)
 {

src/video/mir/SDL_miropengl.h

@@ -33,6 +33,7 @@
 #define MIR_GL_DeleteContext   SDL_EGL_DeleteContext
 #define MIR_GL_GetSwapInterval SDL_EGL_GetSwapInterval
 #define MIR_GL_SetSwapInterval SDL_EGL_SetSwapInterval
+#define MIR_GL_UnloadLibrary   SDL_EGL_UnloadLibrary
 
 extern int
 MIR_GL_SwapWindow(_THIS, SDL_Window* window);