time to remove commoncrypto, fare thee well (#3551)

* time to remove commoncrypto, fare thee well

* remove even more

* update the changelog

* remove more things

* don't need this function

* remove CAST5 CTR tests since that was only supported in commoncrypto

* assert a thing
diff --git a/tests/hazmat/primitives/utils.py b/tests/hazmat/primitives/utils.py
index 5932636..b820012 100644
--- a/tests/hazmat/primitives/utils.py
+++ b/tests/hazmat/primitives/utils.py
@@ -47,10 +47,9 @@
 
 
 def encrypt_test(backend, cipher_factory, mode_factory, params):
-    if not backend.cipher_supported(
+    assert backend.cipher_supported(
         cipher_factory(**params), mode_factory(**params)
-    ):
-        pytest.skip("cipher/mode combo is unsupported by this backend")
+    )
 
     plaintext = params["plaintext"]
     ciphertext = params["ciphertext"]