[rubygems/rubygems] Remove more compatibility code with old RubyGems

https://github.com/rubygems/rubygems/commit/74e8eff779

lib/bundler/rubygems_integration.rb

@@ -57,15 +57,6 @@ module Bundler
       nil
     end
 
-    def spec_missing_extensions?(spec, default = true)
-      return spec.missing_extensions? if spec.respond_to?(:missing_extensions?)
-
-      return false if spec.default_gem?
-      return false if spec.extensions.empty?
-
-      default
-    end
-
     def stub_set_spec(stub, spec)
       stub.instance_variable_set(:@spec, spec)
     end

lib/bundler/source/git.rb

@@ -210,7 +210,7 @@ module Bundler
           checkout
         end
 
-        generate_bin_options = { disable_extensions: !Bundler.rubygems.spec_missing_extensions?(spec), build_args: options[:build_args] }
+        generate_bin_options = { disable_extensions: !spec.missing_extensions?, build_args: options[:build_args] }
         generate_bin(spec, generate_bin_options)
 
         requires_checkout? ? spec.post_install_message : nil

lib/bundler/source/rubygems.rb

@@ -357,7 +357,7 @@ module Bundler
         @installed_specs ||= Index.build do |idx|
           Bundler.rubygems.installed_specs.reverse_each do |spec|
             spec.source = self
-            if Bundler.rubygems.spec_missing_extensions?(spec, false)
+            if spec.missing_extensions?
               Bundler.ui.debug "Source #{self} is ignoring #{spec} because it is missing extensions"
               next
             end