Make Valine available

[sli1989]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines.
• Tests for the changes was maked (for bug fixes / features).
  • Muse | Mist have been tested.
  • Pisces | Gemini have been tested.
• Docs in NexT website have been added / updated (for features).

PR Type

What kind of change does this PR introduce?

• Bugfix.
• Feature.
• Code style update (formatting, local variables).
• Refactoring (no functional changes, no api changes).
• Build related changes.
• CI related changes.
• Documentation content changes.
• Other... Please describe:

What is the current behavior?

Issue resolved: #922

What is the new behavior?

With the Fix of unreachable issue with LeanCloud service in Valine, the new Valine will automatically introduce av-min.js.
So delete the section of av-min.js in Valine

• Screenshots with this changes: N/A
• Link to demo site with this changes: N/A

How to use?

In NexT _config.yml:

...

Does this PR introduce a breaking change?

• Yes.
• No.

[CLAassistant]

All committers have signed the CLA.

[sli1989]

@xCss Need your review, thanks.

[xCss]

I think it can be modified to be configurable here.

[stevenjoezhang]

hexo-theme-next/_config.yml

Lines 1161 to 1166 in 7eaf354

	# leancloud-storage
	# See: https://www.npmjs.com/package/leancloud-storage
	# Example:
	# leancloud: //cdn.jsdelivr.net/npm/leancloud-storage@3/dist/av-min.js
	leancloud: