[Misc][LoRA] Refactor and clean MergedQKVParallelLinearWithLora implementation

[Isotr0py]

This PR aims to clean up MergedColumnParallelLinearWithLora and MergedQKVParallelLinearWithLora implementation

• MergedQKVParallelLinearWithLora has a similar weights initialization with MergedColumnParallelLinearWithLora, and we can treat it as a special case of MergedColumnParallelLinearWithLora with arbitrary shard_size.
• Therefore, we can further clean up MergedQKVParallelLinearWithLora implementation based on MergedColumnParallelLinearWithLora.

[github-actions]

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[jeejeelee]

Thanks four your clean up, LGTM