docs: update two references to the removed 'mad' plugin

https://bugzilla.gnome.org/show_bug.cgi?id=776140

ext/soup/gstsouphttpsrc.c

@@ -43,8 +43,8 @@
  * |[
  * gst-launch-1.0 -v souphttpsrc user-agent="FooPlayer 0.99 beta"
  *     automatic-redirect=false proxy=http://proxy.intranet.local:8080
- *     location=http://music.foobar.com/demo.mp3 ! mad ! audioconvert
- *     ! audioresample ! alsasink
+ *     location=http://music.foobar.com/demo.mp3 ! mpgaudioparse
+ *     ! mpg123audiodec ! audioconvert ! audioresample ! autoaudiosink
  * ]| The above pipeline will read and decode and play an mp3 file from a
  * web server using the HTTP protocol. If the server sends redirects,
  * the request fails instead of following the redirect. The specified

gst/audioparsers/gstmpegaudioparse.c

@@ -29,7 +29,8 @@
  * <refsect2>
  * <title>Example launch line</title>
  * |[
- * gst-launch-1.0 filesrc location=test.mp3 ! mpegaudioparse ! mad ! autoaudiosink
+ * gst-launch-1.0 filesrc location=test.mp3 ! mpegaudioparse ! mpg123audiodec
+ *  ! audioconvert ! audioresample ! autoaudiosink
  * ]|
  * </refsect2>
  */