Remove unused HTML Validator (#23866)

app/validators/html_validator.rb

@@ -1,20 +0,0 @@
-# frozen_string_literal: true
-
-class HtmlValidator < ActiveModel::EachValidator
-  ERROR_RE = /Opening and ending tag mismatch|Unexpected end tag/
-
-  def validate_each(record, attribute, value)
-    return if value.blank?
-
-    errors = html_errors(value)
-
-    record.errors.add(attribute, I18n.t('html_validator.invalid_markup', error: errors.first.to_s)) unless errors.empty?
-  end
-
-  private
-
-  def html_errors(str)
-    fragment = Nokogiri::HTML.fragment(options[:wrap_with] ? "<#{options[:wrap_with]}>#{str}</#{options[:wrap_with]}>" : str)
-    fragment.errors.select { |error| ERROR_RE.match?(error.message) }
-  end
-end