Deleted fun_treemap

@thestinger and I talked about this in IRC. There are a couple of use
cases for a persistent map, but they aren't common enough to justify
inclusion in libextra and vary enough that they would require multiple
implementations anyways.

In any case, fun_treemap in its current state is basically useless.

Author: sfackler

src/libextra/extra.rs

@@ -55,7 +55,6 @@ pub mod flatpipes;
 
 pub mod container;
 pub mod bitv;
-pub mod fun_treemap;
 pub mod list;
 pub mod ringbuf;
 pub mod priority_queue;