Avoid duplicate RSC install warning command

Author: justin808

react_on_rails/lib/generators/react_on_rails/js_dependency_manager.rb

@@ -464,8 +464,7 @@ def rsc_dependency_pin_failed_warning
           "All RSC projects are temporarily pinned to that version because the unversioned " \
           "`latest` tag may not export react-on-rails-rsc/RspackPlugin until stable 19.0.5 " \
           "is published, so the generator left the version pin in package.json rather than " \
-          "install a potentially incompatible version. " \
-          "Run #{manual_add_packages_command(rsc_packages_with_pin)} to finish setup."
+          "install a potentially incompatible version."
       end
 
       def remove_base_package_if_present

react_on_rails/spec/react_on_rails/generators/js_dependency_manager_spec.rb

@@ -700,6 +700,7 @@ def errors
       expect(warning_text).to include("react-on-rails-rsc/RspackPlugin")
       # the manual instruction points at the pinned version, not the unversioned package
       expect(warning_text).to include("npm install --save-exact react-on-rails-rsc@19.0.5-rc.6")
+      expect(warning_text.scan("npm install --save-exact react-on-rails-rsc@19.0.5-rc.6").size).to eq(1)
     end
 
     it "keeps the rspack pin in the manual install instruction when the pinned install raises" do