Remove WordPressVIPMinimum.Variables.VariableAnalysis

[GaryJones]

What problem would the enhancement address for VIP?

Since VIPCS 3.0 is a major release with breaking changes, we can remove the deprecated WordPressVIPMinimum.Variables.VariableAnalysis sniff completely.

Describe the solution you'd like

Remove the relevant sniff files, test files, ruleset test snippets and corresponding violation line references, and the ruleset XML references.

[GaryJones]

Per #612:

Action plan suggestion:

• Deprecate the sniff in the next release (2.x) by:
  • Adding a deprecation warning to the sniff which will inform people to remove the sniff reference from their own custom ruleset.
  • Silencing all messages from the sniff from within the VIPMinimum ruleset, effectively removing the sniff already for people using the standard rulesets.
• Remove the actual sniff in the next major, i.e. 3.0.0.