hosts.txt: removing mtn.i2p-projekt.i2p and trac.i2p2.i2p (said to be permanently down)

Untested (only checked the monotone tunnel doesn't seem to be in the config for new installations any more). Please double-check these are indeed the ones that are down.

While at it, maybe have a look at anoncoin.i2p as well as exchanged.i2p - reason I am adding this is that I haven't been able to reach those in several tries and didn't find them listed at identiguy any more either (pretty sure they used to be there).