Remove irrelevant FIXME

compiler/rustc_infer/src/infer/mod.rs

@@ -678,8 +678,6 @@ pub fn type_is_unconstrained_numeric(&'a self, ty: Ty<'_>) -> UnconstrainedNumer
 
     pub fn unsolved_variables(&self) -> Vec<Ty<'tcx>> {
         let mut inner = self.inner.borrow_mut();
-        // FIXME(const_generics): should there be an equivalent function for const variables?
-
         let mut vars: Vec<Ty<'_>> = inner
             .type_variables()
             .unsolved_variables()