Bug 1096089: Update webref tests. r=karlt

Generalize [Test remove with a start at the duration.] expected result to all platforms using mp4

testing/web-platform/meta/media-source/mediasource-remove.html.ini

@@ -20,6 +20,6 @@
 
   [Test remove with a start at the duration.]
     expected:
-      if not debug and (os == "win") and (version == "6.2.9200") and (processor == "x86_64") and (bits == 64): FAIL
-      if not debug and (os == "win") and (version == "6.1.7601") and (processor == "x86") and (bits == 32): FAIL
+      if (os == "win") and (version != "5.1.2600"): FAIL
+      if os == "mac": FAIL