Retire Linus' default bridges

Linus mentioned to me that he intends to shut down his default bridges to reduce the maintenance burden and to eliminate the risk of seeing both entry and exit traffic.

The affected bridges are:

• 109.105.109.163:38980
• 109.105.109.163:47779
• 109.105.109.165:10527
• 109.105.109.147:13764

I'll push a patch that removes these four bridges in a second.