remove final traces of mng decoder, part of bug 195280. not part of build.

build/mac/build_scripts/MozillaBuildList.pm

@@ -918,7 +918,6 @@ sub BuildClientDist()
 
     #LIBIMAGE
     InstallFromManifest(":mozilla:modules:libimg:png:MANIFEST",                    "$distdirectory:libimg:");
-    InstallFromManifest(":mozilla:modules:libimg:mng:MANIFEST",                    "$distdirectory:libimg:");
 
     #LIBIMG2
     InstallFromManifest(":mozilla:modules:libpr0n:public:MANIFEST_IDL",            "$distdirectory:libimg2:");