change regression tests for swf, use same as flv, swf muxer only supports mp3

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@7432 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

tests/regression.sh

@@ -650,8 +650,8 @@ do_libav mpg
 # mpegts
 do_libav ts
 
-# swf (decode audio only)
-do_libav swf "-acodec mp2"
+# swf
+do_libav swf -an
 
 # ffm
 do_libav ffm