Reuse common AssetExtract.java

Also removes unused `mActivity` member.
Note we changed the constructor input parameter to accept a `Context`
object which is a parent class of the previous `Activity` one.
Changes were tested on both kivy and service_only bootstraps.
Also removes the `get_common_dir()` as it's no longer used since #2092

pythonforandroid/bootstrap.py

@@ -132,9 +132,6 @@ def get_build_dir(self):
     def get_dist_dir(self, name):
         return join(self.ctx.dist_dir, name)
 
-    def get_common_dir(self):
-        return os.path.abspath(join(self.bootstrap_dir, "..", 'common'))
-
     @property
     def name(self):
         modname = self.__class__.__module__

pythonforandroid/bootstraps/common/build/src/main/java/org/renpy/android/AssetExtract.java

@@ -4,7 +4,7 @@
 
 import java.io.*;
 
-import android.app.Activity;
+import android.content.Context;
 import android.util.Log;
 
 import java.io.BufferedInputStream;
@@ -24,11 +24,9 @@
 public class AssetExtract {
 
     private AssetManager mAssetManager = null;
-    private Activity mActivity = null;
 
-    public AssetExtract(Activity act) {
-        mActivity = act;
-        mAssetManager = act.getAssets();
+    public AssetExtract(Context context) {
+        mAssetManager = context.getAssets();
     }
 
     public boolean extractTar(String asset, String target) {

tests/test_bootstrap.py

@@ -104,9 +104,6 @@ def test_build_dist_dirs(self):
             bs.get_build_dir().endswith("build/bootstrap_builds/sdl2")
         )
         self.assertTrue(bs.get_dist_dir("test_prj").endswith("dists/test_prj"))
-        self.assertTrue(
-            bs.get_common_dir().endswith("pythonforandroid/bootstraps/common")
-        )
 
     def test__cmp_bootstraps_by_priority(self):
         # Test service_only has higher priority than sdl2: