Remove need for Natalie patches

Rakefile

@@ -1,7 +1,6 @@
 # frozen_string_literal: true
 
 require "bundler/gem_tasks"
-require "rake/extensiontask"
 require "rake/clean"
 
 task default: %i[compile test]
@@ -27,14 +26,16 @@ task build: [:check_manifest, :templates]
 task "compile:prism" => ["templates"] # must be before the ExtensionTask is created
 
 if RUBY_ENGINE == "ruby" and !ENV["PRISM_FFI_BACKEND"]
+  require "rake/extensiontask"
+
   Rake::ExtensionTask.new(:compile) do |ext|
     ext.name = "prism"
     ext.ext_dir = "ext/prism"
     ext.lib_dir = "lib/prism"
     ext.gem_spec = Gem::Specification.load("prism.gemspec")
   end
 elsif RUBY_ENGINE == "jruby"
-  require 'rake/javaextensiontask'
+  require "rake/javaextensiontask"
 
   # This compiles java to make sure any templating changes produces valid code.
   Rake::JavaExtensionTask.new(:compile) do |ext|

lib/prism/polyfill/string.rb

@@ -1,7 +1,9 @@
 # frozen_string_literal: true
 
-# Polyfill for String#unpack1 with the offset parameter.
-if String.instance_method(:unpack1).parameters.none? { |_, name| name == :offset }
+# Polyfill for String#unpack1 with the offset parameter. Not all Ruby engines
+# have Method#parameters implemented, so we check the arity instead if
+# necessary.
+if (unpack1 = String.instance_method(:unpack1)).respond_to?(:parameters) ? unpack1.parameters.none? { |_, name| name == :offset } : (unpack1.arity == 1)
   String.prepend(
     Module.new {
       def unpack1(format, offset: 0) # :nodoc: