chore: remove obsolete prepublish hook (#4002)

The prepublish hook was previously needed to merge onPublish fields into
package.json before publishing (changing 'main' from src/index.ts to
lib-commonjs/index.js).

This is no longer needed because:
1. All packages now have proper exports field pointing to built files
2. main, module, and types fields already point to lib/ and lib-commonjs/
3. No packages have onPublish fields anymore (verified with grep)

The postbump hook is retained as it's still needed for updating
dependency-profiles after version bumps.

Author: Saadnajmi

beachball.config.js

@@ -5,15 +5,6 @@ const execSync = require('child_process').execSync;
 module.exports = {
   disallowedChangeTypes: ['major'],
   hooks: {
-    prepublish: (packagePath) => {
-      const packageJsonPath = path.join(packagePath, 'package.json');
-      const packageJson = JSON.parse(fs.readFileSync(packageJsonPath, 'utf-8'));
-      if (packageJson.onPublish) {
-        Object.assign(packageJson, packageJson.onPublish);
-        delete packageJson.onPublish;
-        fs.writeFileSync(packageJsonPath, JSON.stringify(packageJson, null, 2) + '\n');
-      }
-    },
     postbump: (packagePath, name) => {
       if (name === '@fluentui-react-native/dependency-profiles') {
         console.log(`Updating ${name} to use latest published versions`);