Disable `CODE_SIGN_IDENTITY` for `iphoneos`

This sets `CODE_SIGN_IDENTITY` to empty for all generated aggregate and
Pod targets.

lib/cocoapods/installer/xcode/pods_project_generator/aggregate_target_installer.rb

@@ -45,6 +45,7 @@ module Pod
           #
           def custom_build_settings
             settings = {
+              'CODE_SIGN_IDENTITY[sdk=iphoneos*]' => '',
               'MACH_O_TYPE'                       => 'staticlib',
               'OTHER_LDFLAGS'                     => '',
               'OTHER_LIBTOOLFLAGS'                => '',

lib/cocoapods/installer/xcode/pods_project_generator/pod_target_installer.rb

@@ -54,6 +54,7 @@ module Pod
               settings['PRIVATE_HEADERS_FOLDER_PATH'] = ''
               settings['PUBLIC_HEADERS_FOLDER_PATH'] = ''
             end
+            settings['CODE_SIGN_IDENTITY[sdk=iphoneos*]'] = ''
             settings
           end