Bug 1395393 - Fix bustage on a CLOSED TREE.

MozReview-Commit-ID: BI4fIMikA0J

media/libcubeb/src/moz.build

@@ -13,8 +13,7 @@ SOURCES += [
     'cubeb_log.cpp',
     'cubeb_mixer.cpp',
     'cubeb_panner.cpp',
-    'cubeb_strings.c',
-    'cubeb_utils.c'
+    'cubeb_strings.c'
 ]
 
 if CONFIG['MOZ_ALSA']: