fix: remove unneccessary dependencies

[mpetrunic]

Can we remove private key signing altogether or move it to different package?

Description

Related Issue Or Context

Closes: #

How Has This Been Tested? Testing details.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation

Checklist:

• I have commented my code, particularly in hard-to-understand areas.
• I have ensured that all acceptance criteria (or expected behavior) from issue are met
• I have updated the documentation locally and in chainbridge-docs.
• I have added tests to cover my changes.
• I have ensured that all the checks are passing and green, I've signed the CLA bot

[MakMuftic]

Remove it altogether, as fee oracle is the one signing this information - never SDK. I guess this flow is here from the time that our local setup with fee oracle was still being worked on - @wainola @enemycnt please confirm this.