Remove charset declaration from Android MIME type

Android apps are binary blobs, not UTF-8. It's possible that the
archive includes byte sequences that are invalid UTF-8 and we can't
expect clients to do the right thing when they encounter such data.

Change-Id: Iad16c06f7e977c44e2c71ab3f7952036a03fb22e

appinventor/appengine/src/com/google/appinventor/shared/storage/StorageUtil.java

@@ -121,7 +121,7 @@ public class StorageUtil {
     }
 
     if (filePath.endsWith(".apk")) {
-      return "application/vnd.android.package-archive; charset=utf-8";
+      return "application/vnd.android.package-archive";
     }
 
     if (filePath.endsWith(".aia")) {

appinventor/appengine/tests/com/google/appinventor/server/DownloadServletTest.java

@@ -132,7 +132,7 @@ public class DownloadServletTest {
     MockHttpServletResponse response = new MockHttpServletResponse();
     download.doGet(request, response);
     checkResponseHeader(response, "attachment; filename=\"filename123.apk\"");
-    assertEquals("application/vnd.android.package-archive; charset=utf-8",
+    assertEquals("application/vnd.android.package-archive",
         response.getContentType());
     PowerMock.verifyAll();
   }
@@ -148,7 +148,7 @@ public class DownloadServletTest {
     MockHttpServletResponse response = new MockHttpServletResponse();
     download.doGet(request, response);
     checkResponseHeader(response, "attachment; filename=\"filename123.apk\"");
-    assertEquals("application/vnd.android.package-archive; charset=utf-8",
+    assertEquals("application/vnd.android.package-archive",
         response.getContentType());
     PowerMock.verifyAll();
   }

appinventor/appengine/tests/com/google/appinventor/shared/storage/StorageUtilTest.java

@@ -49,7 +49,7 @@ public class StorageUtilTest extends TestCase {
     assertEquals("image/jpeg", StorageUtil.getContentTypeForFilePath("kitty.jpg"));
     assertEquals("image/jpeg", StorageUtil.getContentTypeForFilePath("kitty.jpeg"));
     assertEquals("image/png", StorageUtil.getContentTypeForFilePath("kitty.png"));
-    assertEquals("application/vnd.android.package-archive; charset=utf-8",
+    assertEquals("application/vnd.android.package-archive",
         StorageUtil.getContentTypeForFilePath("HelloPurr.apk"));
     assertEquals("application/zip; charset=utf-8",
         StorageUtil.getContentTypeForFilePath("HelloPurr.aia"));