Remove an xfail-fast, as this seems to work on Windows now

Author: catamorphism

src/test/run-pass/class-separate-impl.rs

@@ -1,5 +1,3 @@
-// xfail-fast
-// (Not sure why, though -- FIXME (tjc)
 import to_str::*;
 import to_str::to_str;