Remove warning when renderer is not OpenGL

Trilinear filtering can currently only be enabled for OpenGL renderers.

Do not print a warning if the renderer is not OpenGL, as it can confuses
users, while nothing is wrong.

app/src/screen.c

@@ -305,7 +305,7 @@ screen_init_rendering(struct screen *screen, const char *window_title,
             LOGI("Trilinear filtering disabled");
         }
     } else {
-        LOGW("Trilinear filtering disabled (not an OpenGL renderer)");
+        LOGD("Trilinear filtering disabled (not an OpenGL renderer)");
     }
 
     SDL_Surface *icon = read_xpm(icon_xpm);