remove Haml::Util.av_template_class

This method previously existed to hide the complexity of different
ActionView Template base classes in different rails versions. Since
that is no longer the case, it is simpler to remove it and use
ActionView::Template::Error.

lib/haml/util.rb

@@ -56,15 +56,6 @@ module Haml
       $stderr = the_real_stderr
     end
 
-    # Returns an ActionView::Template::* class.
-    # These classes are of the form `ActionView::Template::Foo`.
-    #
-    # @param name [#to_s] The name of the class to get.
-    #   For example, `:Error` will return `ActionView::Template::Error`.
-    def av_template_class(name)
-      ActionView::Template.const_get(name.to_s)
-    end
-
     ## Rails XSS Safety
 
     # Whether or not ActionView's XSS protection is available and enabled,

test/helper_test.rb

@@ -95,7 +95,7 @@ HAML
 
     begin
       ActionView::Base.new.render(:inline => "<%= flatten('Foo\\nBar') %>")
-    rescue NoMethodError, Haml::Util.av_template_class(:Error)
+    rescue NoMethodError, ActionView::Template::Error
       proper_behavior = true
     end
     assert(proper_behavior)

test/template_test.rb

@@ -91,7 +91,7 @@ class TemplateTest < MiniTest::Unit::TestCase
         assert_equal(pair.first, pair.last, message)
       end
     end
-  rescue Haml::Util.av_template_class(:Error) => e
+  rescue ActionView::Template::Error => e
     if e.message =~ /Can't run [\w:]+ filter; required (one of|file) ((?:'\w+'(?: or )?)+)(, but none were found| not found)/
       puts "\nCouldn't require #{$2}; skipping a test."
     else