ref(pkg/smi): remove unused kubeClient from smi client

[fristonio]

Description:

This PR removes the unused kubeClient from SMI client in pkg/smi/client.go.
Found while navigating the source code.

Testing done:

Existing unit tests in client_tests.go should be enough for the changeset.

Affected area:

Functional Area
New Functionality	[ ]
CI System	[ ]
CLI Tool	[ ]
Certificate Management	[ ]
Control Plane	[ ]
Demo	[ ]
Documentation	[ ]
Egress	[ ]
Ingress	[ ]
Install	[ ]
Networking	[ ]
Observability	[ ]
Performance	[ ]
SMI Policy	[ ]
Security	[ ]
Sidecar Injection	[ ]
Tests	[ ]
Upgrade	[ ]
Other	[ x ]

Please answer the following questions with yes/no.

1. Does this change contain code from or inspired by another project?
   • Did you notify the maintainers and provide attribution?

Not inspired by any external source code.

2. Is this a breaking change?

No

4. Has documentation corresponding to this change been updated in the osm-docs repo (if applicable)?

No need for a documentation change, internal refactoring of SMI client.

[nojnhuh]

LGTM. Thanks @fristonio!

[trstringer]

Thank you for the contribution!