Remove tri.rs and four.rs

Closes #1892

Author: marijnh

src/libstd/four.rs

@@ -14,7 +14,7 @@ use core(vers = "0.2");
 import core::*;
 
 export net, uv;
-export c_vec, four, tri, util;
+export c_vec, util;
 export bitv, deque, fun_treemap, list, map, smallintmap, sort, treemap, ufind;
 export rope, arena;
 export ebml, dbg, getopts, json, rand, sha1, term, time, prettyprint;
@@ -33,8 +33,6 @@ mod uv_hl;
 // Utility modules
 
 mod c_vec;
-mod four;
-mod tri;
 mod util;