fix: Drop reel integration

Reel has been unmaintained since 2016, and we can stop supporting it in the upcoming version of Sinatra.

Gemfile

@@ -58,7 +58,6 @@ if RUBY_ENGINE == "ruby"
   gem 'erubis'
   gem 'haml', '>= 3.0'
   gem 'sass'
-  gem 'reel-rack'
   gem 'celluloid', '~> 0.16.0'
   gem 'commonmarker', '~> 0.20.0'
   gem 'pandoc-ruby', '~> 2.0.2'

lib/sinatra/base.rb

@@ -1832,7 +1832,6 @@ module Sinatra
 
     ruby_engine = defined?(RUBY_ENGINE) && RUBY_ENGINE
 
-    server.unshift 'reel'
     server.unshift 'puma'
     server.unshift 'mongrel'  if ruby_engine.nil?
     server.unshift 'thin'     if ruby_engine != 'jruby'

test/integration_helper.rb

@@ -81,10 +81,6 @@ module IntegrationHelper
       name.to_s == "puma"
     end
 
-    def reel?
-      name.to_s == "reel"
-    end
-
     def trinidad?
       name.to_s == "trinidad"
     end

test/integration_test.rb

@@ -17,7 +17,7 @@ class IntegrationTest < Minitest::Test
     random = "%064x" % Kernel.rand(2**256-1)
     server.get "/ping?x=#{random}"
     count = server.log.scan("GET /ping?x=#{random}").count
-    if server.net_http_server? || server.reel?
+    if server.net_http_server?
       assert_equal 0, count
     elsif server.webrick?
       assert(count > 0)
@@ -47,13 +47,13 @@ class IntegrationTest < Minitest::Test
     }ix
 
     # because Net HTTP Server logs to $stderr by default
-    assert_match exp, server.log unless server.net_http_server? || server.reel? || server.rainbows?
+    assert_match exp, server.log unless server.net_http_server? || server.rainbows?
   end
 
   it 'does not generate warnings' do
     assert_raises(OpenURI::HTTPError) { server.get '/' }
     server.get '/app_file'
-    assert_equal [], server.warnings unless server.reel?
+    assert_equal [], server.warnings
   end
 
   it 'sets the Content-Length response header when sending files' do