Revert "Document rscBundle parameter's Sub-PR 3 role"

This reverts commit a7734472b8e9e2bf80088a85ef0b7b9dd76b44a0.

The `rscBundle = false` parameter shape follows the documented Pro
pattern: docs/oss/migrating/rsc-preparing-app.md:244 and
docs/pro/react-server-components/upgrading-existing-pro-app.md:106
both name it by parameter name and show the exact
`if (!rscBundle) { ... RSCWebpackPlugin ... }` guard. The Pro dummy
(react_on_rails_pro/spec/dummy/config/webpack/serverWebpackConfig.js)
uses the same shape with no inline comment.

The reverted commit restated what the docs already cover and added a
Sub-PR 3 reference that would rot once Sub-PR 3 merges. Code follows
documented conventions; readers who need context can read the doc.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: ihabadham

config/webpack/serverWebpackConfig.js

@@ -16,10 +16,6 @@ function extractLoader(rule, loaderName) {
   });
 }
 
-// rscBundle: set to true in Sub-PR 3 for the RSC client-reference bundle,
-// which handles RSCWebpackPlugin(isServer: false) separately. Default
-// false builds the SSR bundle with RSCWebpackPlugin(isServer: true).
-// Follows the Pro dummy's `serverWebpackConfig(rscBundle)` pattern.
 const configureServer = (rscBundle = false) => {
   const bundler = getBundler();