Wemake-python-styleguide: Remove flake8-coding

[sobolevn]

We need to vendor this dependency to our own codebase:

• create new violation
• create new logical check
• write tests
• copy configuration

Implementation: https://github.com/tk0miya/flake8-coding/blob/master/flake8_coding.py#L52-L73

Related: #1139

[orsinium]

Is explicit encoding still actual? In Python 3 it's UTF-8 by default, and there is no reason to make it non-UTF.

The default encoding for Python source code is UTF-8

• https://docs.python.org/3/howto/unicode.html

[sobolevn]

I start to agree with this point. We can completely remove this plugin.

But, I am kind of used to this little line 😢
# -*- coding: utf-8 -*-

[orsinium]

We're just too old. Soon we'll be changed by the generation that has never seen Python 2 and hacks around encodings :grinning:

[Kvm99]

Hi! Could I take the issue?

[sobolevn]

Thanks a lot! Assigned.

[sobolevn]

@Kvm99 we would also need to remove EmptyLineAfterCodingViolation