remove a test checking that the hash for bit sets of different domain

sizes are different

The new implementation of DenseBitSet doesn't store the exact domain
size, so of course the hash values for identical sets with different
domain sizes may be equal.

Author: Tage Johansson

compiler/rustc_data_structures/src/stable_hasher/tests.rs

@@ -14,16 +14,6 @@ fn hash<T: HashStable<()>>(t: &T) -> Hash128 {
     h.finish()
 }
 
-// Check that bit set hash includes the domain size.
-#[test]
-fn test_hash_bit_set() {
-    use rustc_index::bit_set::DenseBitSet;
-    let a: DenseBitSet<usize> = DenseBitSet::new_empty(1);
-    let b: DenseBitSet<usize> = DenseBitSet::new_empty(2);
-    assert_ne!(a, b);
-    assert_ne!(hash(&a), hash(&b));
-}
-
 // Check that bit matrix hash includes the matrix dimensions.
 #[test]
 fn test_hash_bit_matrix() {