polkadot-omni-node-lib: remove unused dep (#6889)

# Description

Redundant dep that made its way in #6450 . 😅

. It can be
brought up when using `cargo udeps`. Added a github action that runs
`cargo udeps` on the repo too.

## Integration

N/A

## Review Notes

N/A

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Signed-off-by: Iulian Barbu <[email protected]>
Co-authored-by: Bastian Köcher <[email protected]>