android: use os.NativeActivity (#466)

Author: larpon

src/ui_android.c.v

@@ -1,9 +1,9 @@
 module ui
 
+import os
 import sokol.sapp
 
 #include <android/configuration.h>
-#include <android/native_activity.h>
 
 enum AndroidConfig {
 	orientation
@@ -20,15 +20,9 @@ fn C.AConfiguration_getTouchscreen(voidptr) u32
 fn C.AConfiguration_getScreenSize(voidptr) u32
 fn C.AConfiguration_getSdkVersion(voidptr) u32
 
-struct C.AAssetManager {}
-
-struct C.ANativeActivity {
-	assetManager voidptr
-}
-
 pub fn android_config(mode AndroidConfig) u32 {
 	config := C.AConfiguration_new()
-	activity := &C.ANativeActivity(sapp.android_get_native_activity())
+	activity := &os.NativeActivity(sapp.android_get_native_activity())
 	C.AConfiguration_fromAssetManager(config, activity.assetManager)
 	mut cfg := u32(0)
 	match mode {