core: Remove empty bessel mod

Author: brson

src/libcore/bessel.rs

@@ -34,7 +34,6 @@ export either, option, result, iter;
 export libc, os, ctypes, sys, unsafe, logging;
 export comm, task, future;
 export extfmt;
-export bessel;
 export tuple;
 export to_str;
 
@@ -43,7 +42,6 @@ export to_str;
 mod box;
 mod char;
 mod float;
-mod bessel;
 mod f32;
 mod f64;
 mod int;