Remove benchmark dependency

Ruby wants to bundle it: ruby/ruby#11492

This is pretty much all the gem does anyways: https://github.com/ruby/benchmark/blob/8d2c8a0d7ca72bff7e97a4800e16c72f232867e4/lib/benchmark.rb#L311-L315

I removed the `bench_cop` rake task since it uses `benchmark` and I believe it just isn't very useful.
Dedicated tools like `vernier` or `stackprof` (which has buildin support in RuboCop these days)
are much more suited for the task.

Rakefile

@@ -32,49 +32,6 @@ task default: %i[documentation_syntax_check spec prism_spec internal_investigati
 require 'yard'
 YARD::Rake::YardocTask.new
 
-desc 'Benchmark a cop on given source file/dir'
-task :bench_cop, %i[cop srcpath times] do |_task, args|
-  require 'benchmark'
-  require 'rubocop'
-  include RuboCop
-  include RuboCop::Formatter::TextUtil
-
-  cop_name = args[:cop]
-  src_path = args[:srcpath]
-  iterations = args[:times] ? Integer(args[:times]) : 1
-
-  cop_class = if cop_name.include?('/')
-                Cop::Registry.all.find { |klass| klass.cop_name == cop_name }
-              else
-                Cop::Registry.all.find { |klass| klass.cop_name[/[a-zA-Z]+$/] == cop_name }
-              end
-  raise "No such cop: #{cop_name}" if cop_class.nil?
-
-  config = ConfigLoader.load_file(ConfigLoader::DEFAULT_FILE)
-  cop = cop_class.new(config)
-
-  puts "Benchmarking #{cop.cop_name} on #{src_path} (using default config)"
-
-  files = if File.directory?(src_path)
-            Dir[File.join(src_path, '**', '*.rb')]
-          else
-            [src_path]
-          end
-
-  puts "(#{pluralize(iterations, 'iteration')}, #{pluralize(files.size, 'file')})"
-
-  ruby_version = RuboCop::TargetRuby.supported_versions.last
-  srcs = files.map { |file| ProcessedSource.from_file(file, ruby_version) }
-
-  puts 'Finished parsing source, testing inspection...'
-  puts(Benchmark.measure do
-    iterations.times do
-      commissioner = Cop::Commissioner.new([cop], [])
-      srcs.each { |src| commissioner.investigate(src) }
-    end
-  end)
-end
-
 desc 'Syntax check for the documentation comments'
 task documentation_syntax_check: :yard_for_generate_documentation do
   require 'parser/ruby25'

exe/rubocop

@@ -11,13 +11,14 @@ exit exit_status if server_cli.exit?
 if RuboCop::Server.running?
   exit_status = RuboCop::Server::ClientCommand::Exec.new.run
 else
-  require 'benchmark'
   require 'rubocop'
 
   cli = RuboCop::CLI.new
 
-  time = Benchmark.realtime { exit_status = cli.run }
+  time_start = Process.clock_gettime(Process::CLOCK_MONOTONIC)
+  exit_status = cli.run
+  elapsed_time = Process.clock_gettime(Process::CLOCK_MONOTONIC) - time_start
 
-  puts "Finished in #{time} seconds" if cli.options[:debug] || cli.options[:display_time]
+  puts "Finished in #{elapsed_time} seconds" if cli.options[:debug] || cli.options[:display_time]
 end
 exit exit_status