Given the prefix, you might think this term has something to do with being oppositional. But here, the operative meaning is apart or away. As for mediation, well, one guess is as good as another.
Disintermediation, in fact, has been practiced in recent years because of the global financial crisis.
It is the movement of savings or investment funds away from institutions such as banks into higher-yielding investments in the securities markets, such as Treasurys.