Remove unneeded HAML upgrade script

We updated a long time ago and I now copied those scripts to a Gist to
share with others:

* https://gist.github.com/mkllnk/bab2d474d686a2e3b88914129aee63e1

spec/lib/haml_up_spec.rb

@@ -1,50 +0,0 @@
-# frozen_string_literal: true
-
-require 'spec_helper'
-require 'haml_up'
-
-RSpec.describe HamlUp, skip: !Gem::Dependency.new("", "~> 5.2").match?("", Haml::VERSION) do
-  describe "#rewrite_template" do
-    it "preserves a simple template" do
-      original = "%p This is a paragraph"
-      template = call(original)
-      expect(template).to eq original
-    end
-
-    it "rewrites non-standard attribute hashes" do
-      original = "%p{ng: {click: 'action', show: 'condition'}} label"
-      template = call(original)
-      expect(template).to eq "%p{ \"ng-click\": 'action', \"ng-show\": 'condition' } label"
-    end
-
-    it "preserves standard attribute hashes" do
-      original = "%p{data: {click: 'action', show: 'condition'}} label"
-      template = call(original)
-      expect(template).to eq original
-    end
-
-    it "preserves standard attribute hashes while rewriting others" do
-      original = "%p{data: {click: 'standard'}, ng: {click: 'not'}} label"
-      template = call(original)
-      expect(template).to eq "%p{ data: {click: 'standard'}, \"ng-click\": 'not' } label"
-    end
-
-    it "rewrites multi-line attributes" do
-      original = <<~HAML
-        %li{ ng: { class: "{active: selector.active}" } }
-          %a{ tooltip: "{{selector.object.value}}", "tooltip-placement": "bottom",
-            ng: { transclude: true, class: "{active: selector.active, 'has-tip': selector.object.value}" } }
-      HAML
-      expected = <<~HAML
-        %li{ "ng-class": "{active: selector.active}" }
-          %a{ tooltip: "{{selector.object.value}}", "tooltip-placement": "bottom", "ng-transclude": true, "ng-class": "{active: selector.active, 'has-tip': selector.object.value}" }
-      HAML
-      template = call(original)
-      expect(template).to eq expected
-    end
-
-    def call(original)
-      original.dup.tap { |t| subject.rewrite_template(t) }
-    end
-  end
-end