Remove advertised bandwidth fraction graph from Globe

The advertised bandwidth fraction graph is going to be removed from Onionoo as part of legacy/trac#13674 (moved). We should replace it with the middle probability graph. Will attach a patch in a second.

Setting priority to major, because I'm holding back legacy/trac#13674 (moved) until this patch is merged, so that Globe doesn't look broken. (It's an optional field in Onionoo, so Globe should not rely on it.)

Thanks in advance!