Issue #80 - De-unify dom/media part 1

This de-unifies up to and including dom/media/platforms with the exception of
dom/media/platforms/wmf, because that one throws weird errors in the Win
SDK which don't have a clear cause (yet)

dom/media/eme/mediadrm/moz.build

@@ -10,7 +10,7 @@ EXPORTS.mozilla += [
     'MediaDrmProxySupport.h',
 ]
 
-UNIFIED_SOURCES += [
+SOURCES += [
     'MediaDrmCDMCallbackProxy.cpp',
     'MediaDrmCDMProxy.cpp',
     'MediaDrmProxySupport.cpp',

dom/media/eme/moz.build

@@ -23,7 +23,7 @@ EXPORTS.mozilla += [
     'EMEUtils.h',
 ]
 
-UNIFIED_SOURCES += [
+SOURCES += [
     'CDMCaps.cpp',
     'DetailedPromise.cpp',
     'EMEUtils.cpp',