Remove outdated code for Tilt 1.x versions support

I found out that Sinatra codebase still contains code for handling
both versions of Tilt (1.x and 2.x), however starting from Sinatra 2.0
the minimally required version of Tilt is 2.0 as well.

This commit removes old code and cleans up a bit how tests for
different markdown engines are generated.

lib/sinatra/base.rb

@@ -786,15 +786,8 @@ module Sinatra
     def find_template(views, name, engine)
       yield ::File.join(views, "#{name}.#{@preferred_extension}")
 
-      if Tilt.respond_to?(:mappings)
-        Tilt.mappings.each do |ext, engines|
-          next unless ext != @preferred_extension and engines.include? engine
-          yield ::File.join(views, "#{name}.#{ext}")
-        end
-      else
-        Tilt.default_mapping.extensions_for(engine).each do |ext|
-          yield ::File.join(views, "#{name}.#{ext}") unless ext == @preferred_extension
-        end
+      Tilt.default_mapping.extensions_for(engine).each do |ext|
+        yield ::File.join(views, "#{name}.#{ext}") unless ext == @preferred_extension
       end
     end
 

test/markdown_test.rb

@@ -69,17 +69,18 @@ MarkdownTest = proc do
 end
 
 # Will generate RDiscountTest, KramdownTest, etc.
-map = Tilt.respond_to?(:lazy_map) ? Tilt.lazy_map['md'].map(&:first) : Tilt.mappings['md']
+markdown_templates = Tilt.lazy_map['md'].map { |klass, _require_path| klass }
 
-map.each do |t|
+markdown_templates.each do |template_name|
   begin
-    t = eval(t) if t.is_a? String
-    t.new { "" }
-    klass = Class.new(Minitest::Test) { define_method(:engine) { t }}
+    template = Object.const_get(template_name)
+
+    klass = Class.new(Minitest::Test) { define_method(:engine) { template } }
     klass.class_eval(&MarkdownTest)
-    name = t.name[/[^:]+$/].sub(/Template$/, '') << "Test"
+
+    name = template_name.split('::').last.sub(/Template$/, 'Test')
     Object.const_set name, klass
   rescue LoadError, NameError
-    warn "#{$!}: skipping markdown tests with #{t}"
+    warn "#{$!}: skipping markdown tests with #{template_name}"
   end
 end