Remove redundant SCSS @import statements

The sass-resources-loader webpack plugin automatically injects
app-variables.scss into all SCSS files, making manual @import
statements redundant and potentially problematic.

The previous fix attempted to import app-variables.scss to resolve
undefined $bright-color variables, but this caused issues with
React Server Components builds. The variables are already available
through the webpack sass-resources-loader configuration.

Changes:
- spec/dummy/client/app/components/HelloWorld.module.scss: Remove @import
- react_on_rails_pro/spec/dummy/client/app/components/HelloWorld.module.scss: Remove @import

Fixes React Router Sixth Page RSC test failure.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: justin808

react_on_rails_pro/spec/dummy/client/app/components/HelloWorld.module.scss

@@ -1,5 +1,3 @@
-@import "../assets/styles/app-variables.scss";
-
 .brightColor {
   color: $bright-color;
 }

spec/dummy/client/app/components/HelloWorld.module.scss

@@ -1,5 +1,3 @@
-@import "../assets/styles/app-variables.scss";
-
 .brightColor {
   color: $bright-color;
 }