[CDEC-432] Switch JsonLog & Mockable imports from networking to core

[mhuesch]

Description

• Change imports from networking to core (modules now have a Pos.Core. prefix.
• Remove a few dependencies on networking; switch few deps to core.
• Remove ununsed JsonLog/Mockable re-exports.

Linked issue

https://iohk.myjetbrains.com/youtrack/issue/CDEC-432

Type of change

• [~] 🐞 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)
• 🏭 Refactoring that does not change existing functionality but does improve things like code readability, structure etc
• [~] 🔨 New or improved tests for existing code
• [~] ⛑ git-flow chore (backport, hotfix, etc)

Developer checklist

• I have read the style guide document, and my code follows the code style of this project.
• If my code deals with exceptions, it follows the guidelines.
• I have updated any documentation accordingly, if needed. Documentation changes can be reflected in opening a PR on cardanodocs.com, amending the inline Haddock comments, any relevant README file or one of the document listed in the docs directory.

Testing checklist

• I have added tests to cover my changes.
• All new and existing tests passed.
  ^ module-level refactoring (switching imports) - compiler should catch any errors. Existing tests will continue working, and should ensure correctness.