4.0 | Remove previously deprecated code

Removing the deprecated JS sniffs is tracked separately in #442.

List of deprecated code which should be removed in the next major:
- [ ] `WordPressVIPMinimum\Sniffs\Classes\DeclarationCompatibilitySniff::$checkClasses` - deprecated since VIPCS 3.1.0, see #858, related to #234.
- [ ] `WordPressVIPMinimum\Sniffs\Classes\DeclarationCompatibilitySniff::$checkClassesGroups` - deprecated since VIPCS 3.1.0, see #858, related to #234.
- [ ] The complete `WordPressVIPMinimum\Sniffs\Functions\DynamicCalls` sniff - deprecated since VIPCS 3.1.0, see #517 and #865
- [ ] `WordPressVIPMinimum\Sniffs\Performance\TaxonomyMetaInOptionsSniff::$option_functions` - deprecated since VIPCS 3.1.0, see #872, related to #234.
- [ ] `WordPressVIPMinimum\Sniffs\Security\ProperEscapingFunctionSniff::$url_attrs` - deprecated since VIPCS 2.3.1
- [ ] `WordPressVIPMinimum\Sniffs\Security\ProperEscapingFunctionSniff::$attr_endings` - deprecated since VIPCS 2.3.1
- [ ] `WordPressVIPMinimum\Sniffs\Security\ProperEscapingFunctionSniff::attr_expects_url)_` - deprecated since VIPCS 2.3.1
- [ ] `WordPressVIPMinimum\Sniffs\Security\ProperEscapingFunctionSniff::is_html_attr()` - deprecated since VIPCS 2.3.1

まず、一覧にある WordPressVIPMinimum の sniffs と、それらの deprecated members を調査し、続いて参照されている issue #858、#234、#517、#865、#872 を確認して、対象範囲と依存関係を把握します。JavaScript の sniffs は #442 で別途追跡されています。完了とは、一覧にある deprecated な PHP コードが削除され、その別作業を含まないことを意味します。

索引モデルが issue の本文から書いたものです。