libmediatranscoding: Reorganize test assets

Move test_assets filegroup to correct Android.bp

Move test files in assets to a subfolder as needed in
AndroidTestTemplate.xml

Bug: 173627260
Test: Builds

Change-Id: I1e32081a069c4c1b25aa200dcdb165c0feb07b8a
diff --git a/media/libmediatranscoding/transcoder/tests/AndroidTestTemplate.xml b/media/libmediatranscoding/transcoder/tests/AndroidTestTemplate.xml
index a9a7e2e..451d565 100644
--- a/media/libmediatranscoding/transcoder/tests/AndroidTestTemplate.xml
+++ b/media/libmediatranscoding/transcoder/tests/AndroidTestTemplate.xml
@@ -17,9 +17,7 @@
     <option name="test-suite-tag" value="TranscoderTests" />
     <target_preparer class="com.android.tradefed.targetprep.PushFilePreparer">
         <option name="cleanup" value="false" />
-        <option name="push-file"
-            key="assets"
-            value="/data/local/tmp/TranscodingTestAssets" />
+        <option name="push-file" key="TranscodingTestAssets" value="/data/local/tmp/TranscodingTestAssets" />
     </target_preparer>
 
     <test class="com.android.tradefed.testtype.GTest" >