Clean up DashManifestParserTest

Also improve some tests by asserting the parser is left in
the correct position (assertNextTag).

PiperOrigin-RevId: 272614768

library/dash/src/test/assets/sample_mpd_1 → library/dash/src/test/assets/sample_mpd

@@ -102,4 +102,3 @@ http://www.test.com/vtt
         </AdaptationSet>
         </AdaptationSet>
     </Period>
     </Period>
 </MPD>
 </MPD>
-

library/dash/src/test/assets/sample_mpd_4_event_stream → library/dash/src/test/assets/sample_mpd_event_stream

@@ -44,4 +44,3 @@
   </AdaptationSet>
   </AdaptationSet>
  </Period>
  </Period>
 </MPD>
 </MPD>
-

library/dash/src/test/assets/sample_mpd_3_segment_template → library/dash/src/test/assets/sample_mpd_segment_template

@@ -35,4 +35,3 @@
   </AdaptationSet>
   </AdaptationSet>
  </Period>
  </Period>
 </MPD>
 </MPD>
-

library/dash/src/test/assets/sample_mpd_2_unknown_mime_type → library/dash/src/test/assets/sample_mpd_unknown_mime_type

@@ -115,4 +115,3 @@ http://www.test.com/vtt
                 </AdaptationSet>
                 </AdaptationSet>
     </Period>
     </Period>
 </MPD>
 </MPD>
-