Avoid requiring files of the gem in Rakefile to avoid redefined method warnings

Author: eregon

Rakefile

@@ -1,21 +1,20 @@
 version=File.read("#{__dir__}/lib/concurrent-ruby/concurrent/version.rb")[/'(.+)'/,1]orraise
 edge_version=File.read("#{__dir__}/lib/concurrent-ruby-edge/concurrent/edge/version.rb")[/'(.+)'/,1]orraise
-require_relative'lib/concurrent-ruby/concurrent/utility/engine'
 
 core_gemspec=Gem::Specification.loadFile.join(__dir__,'concurrent-ruby.gemspec')
 ext_gemspec=Gem::Specification.loadFile.join(__dir__,'concurrent-ruby-ext.gemspec')
 edge_gemspec=Gem::Specification.loadFile.join(__dir__,'concurrent-ruby-edge.gemspec')
 
 require'rake/javaextensiontask'
 
-ENV['JRUBY_HOME']=ENV['CONCURRENT_JRUBY_HOME']ifENV['CONCURRENT_JRUBY_HOME'] && !Concurrent.on_jruby?
+ENV['JRUBY_HOME']=ENV['CONCURRENT_JRUBY_HOME']ifENV['CONCURRENT_JRUBY_HOME'] && RUBY_ENGINE != 'jruby'
 
 Rake::JavaExtensionTask.new('concurrent_ruby',core_gemspec)do |ext|
 ext.ext_dir='ext/concurrent-ruby'
 ext.lib_dir='lib/concurrent-ruby/concurrent'
 end
 
-unlessConcurrent.on_jruby? || Concurrent.on_truffleruby?
+ifRUBY_ENGINE == 'ruby'
 require'rake/extensiontask'
 
 Rake::ExtensionTask.new('concurrent_ruby_ext',ext_gemspec)do |ext|
@@ -68,7 +67,7 @@ require 'rubygems'
 require'rubygems/package_task'
 
 Gem::PackageTask.new(core_gemspec){}ifcore_gemspec
-Gem::PackageTask.new(ext_gemspec){}ifext_gemspec && !Concurrent.on_jruby?
+Gem::PackageTask.new(ext_gemspec){}ifext_gemspec && RUBY_ENGINE != 'jruby'
 Gem::PackageTask.new(edge_gemspec){}ifedge_gemspec
 
 CLEAN.include(
@@ -97,7 +96,7 @@ begin
 Bundler.with_original_envdo
 Dir.chdir(__dir__)do
 sh"gem install pkg/concurrent-ruby-#{version}.gem"
-sh"gem install pkg/concurrent-ruby-ext-#{version}.gem"ifConcurrent.on_cruby?
+sh"gem install pkg/concurrent-ruby-ext-#{version}.gem"ifRUBY_ENGINE == 'ruby'
 sh"gem install pkg/concurrent-ruby-edge-#{edge_version}.gem"
 ENV['NO_PATH']='true'
 sh'bundle update'