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.

Start by locating the Python KMS keyring code that compares the stored encryption context with the provided context, then compare its behavior with the Java snippets and the referenced KMS context specification. Done means both reserved keys are excluded before comparison and the relevant tests cover the KMSv1 case.

Vom Indexierungsmodell aus dem Issue-Text verfasst.