remove dead links to youtube-dl

Presumably most users will get it from their linux distribution, or
whatever. Don't want to need to keep updating links if they're going to
rot like this.

doc/tips/downloading_podcasts.mdwn

@@ -74,7 +74,7 @@ and transferring to your laptop on demand.
 ## youtube channels
 
 You can also use `git annex importfeed` on youtube channels.
-It will use [youtube-dl](https://rg3.github.io/youtube-dl/) to automatically
+It will use youtube-dl to automatically
 download the videos.
 
 To download a youtube channel, you need to find the feed associated with that

doc/tips/using_the_web_as_a_special_remote.mdwn

@@ -71,8 +71,7 @@ number takes that many paths from the end.
 <a name=videos></a>
 
 There's support for downloading videos from sites like YouTube, Vimeo,
-and many more. This relies on [youtube-dl](https://rg3.github.io/youtube-dl/)
-to download the videos.
+and many more. This relies on youtube-dl to download the videos.
 
 When you have youtube-dl installed, you can just 
 `git annex addurl http://youtube.com/foo` and it will detect that