Remove unused publish Rake namespace (#941)

Removing the old publish Rake tasks namespace.
We now use mono for publishing so this is no longer needed.

Rakefile

@@ -253,90 +253,6 @@ namespace :build do
   end
 end
 
-namespace :publish do
-  # rubocop:disable Lint/ConstantDefinitionInBlock
-  VERSION_FILE = "lib/appsignal/version.rb"
-  CHANGELOG_FILE = "CHANGELOG.md"
-  # rubocop:enable Lint/ConstantDefinitionInBlock
-
-  def changes
-    git_status_to_array(`git status -s -u`)
-  end
-
-  def git_status_to_array(changes)
-    changes.split("\n").each { |change| change.gsub!(/^.. /, "") }
-  end
-
-  def current_branch
-    `git rev-parse --abbrev-ref HEAD`.chomp
-  end
-
-  task :check_requirements do
-    unless changes.empty?
-      puts "ERROR: There should be no uncommitted file changes."
-      exit 1
-    end
-    unless ENV["EDITOR"]
-      puts "ERROR: $EDITOR environment variable should be set."
-      exit 1
-    end
-  end
-
-  task :configure_version do
-    puts "\n# Configuring new gem version"
-
-    system "$EDITOR #{VERSION_FILE}"
-    unless changes.member?(VERSION_FILE)
-      puts "ERROR: Please actually change the gem version in: #{VERSION_FILE}"
-      exit 1
-    end
-
-    puts "\n# Updating the changelog"
-    system "$EDITOR #{CHANGELOG_FILE}"
-  end
-
-  task :push_gem_packages do
-    puts "\n# Pushing gem packages"
-    Dir.chdir("#{File.dirname(__FILE__)}/pkg") do
-      Dir["*.gem"].each do |gem_package|
-        puts "## Publishing gem package: #{gem_package}"
-        result = system "gem push #{gem_package}"
-        raise "Failed to Push gem" unless result
-      end
-    end
-  end
-
-  task :tag_and_push_version do
-    # Make sure to load the new version number
-    Appsignal.send(:remove_const, :VERSION)
-    load File.expand_path(VERSION_FILE)
-    version = "v#{Appsignal::VERSION}"
-
-    begin
-      puts `git commit -am 'Bump to #{version} [ci skip]'`
-      puts "# Creating tag #{version}"
-      puts `git tag #{version}`
-      puts `git push origin #{version}`
-      puts `git push origin #{current_branch}`
-    rescue
-      puts "ERROR: Tag '#{version}' already exists"
-      exit 1
-    end
-  end
-
-  task :build => "build:clean" do
-    # Shell out to build so the new version is loaded in the gemspec.
-    `rake build:all`
-  end
-end
-task :publish => [
-  "publish:check_requirements",
-  "publish:configure_version",
-  "publish:build",
-  "publish:push_gem_packages",
-  "publish:tag_and_push_version"
-]
-
 desc "Install the AppSignal gem, extension and all possible dependencies."
 task :install => "extension:install" do
   Bundler.with_clean_env do