Drop "sokol" chain support

[kamilchodola]

Changes

• Remove sokol chain and all related items/tests/configs/chainspecs etc

Types of changes

What types of changes does your code introduce?

• Bugfix (a non-breaking change that fixes an issue)
• New feature (a non-breaking change that adds functionality)
• Breaking change (a change that causes existing functionality not to work as expected)
• Optimization
• Refactoring
• Documentation update
• Build-related changes
• Other: Drop support of sokol chain

Testing

Requires testing

• Yes
• No

If yes, did you write tests?

• Yes
• No

[kamilchodola]

I've checked that on Launcher and works well.
Built package and tried with --config sokol and it does not work so seems like it is done well.