Clean unused code and fix build warnings in OpenVINO backend

[zhaixuejun1993]

This pull request makes minor refactoring and code cleanup changes to the translate_gated_delta_net and related functions in ggml-openvino. The changes remove an unused variable, make a function static, and clean up some variable declarations.

Code cleanup and refactoring:

• Removed the unused g_shape and kda variables from translate_gated_delta_net, as the per-key-dimension gating logic is not supported in the fused op.
• Removed the unused H_k variable from translate_gated_delta_net.
• Made the translate_gated_delta_net_ref function static to limit its visibility to the current translation unit.## Overview

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