Additionally remove the KMSv1 Reserved EC Key in KmsKeyring

In Java:

```
private static final String KEY_ID_CONTEXT_KEY = "kms_cmk_id";
```

```
//= specification/s3-encryption/materials/s3-kms-keyring.md#kms-context
//# The stored encryption context with the two reserved keys removed MUST match the provided encryption context.
materialsEncryptionContextCopy.remove(KEY_ID_CONTEXT_KEY);
materialsEncryptionContextCopy.remove(ENCRYPTION_CONTEXT_ALGORITHM_KEY);
```

https://github.com/aws/amazon-s3-encryption-client-python/pull/143 points out we don't currently do this in Python.