Delete unused objective-c++ files (#631)

## Description

As in the title, utils defined in the `ios/RnExecutorch/utils` are not
longer used so they can be deleted.

### Introduces a breaking change?

- [ ] Yes
- [X] No

### Type of change

- [ ] Bug fix (change which fixes an issue)
- [ ] New feature (change which adds functionality)
- [ ] Documentation update (improves or adds clarity to existing
documentation)
- [x] Other (chores, tests, code style improvements etc.)

### Tested on

- [ ] iOS
- [ ] Android

### Testing instructions

<!-- Provide step-by-step instructions on how to test your changes.
Include setup details if necessary. -->

### Screenshots

<!-- Add screenshots here, if applicable -->

### Related issues

<!-- Link related issues here using #issue-number -->

### Checklist

- [ ] I have performed a self-review of my code
- [ ] I have commented my code, particularly in hard-to-understand areas
- [ ] I have updated the documentation accordingly
- [ ] My changes generate no new warnings

### Additional notes

<!-- Include any additional information, assumptions, or context that
reviewers might need to understand this PR. -->

Author: msluszniak

.github/workflows/build-ios-llm-example.yml

@@ -56,24 +56,10 @@ jobs:
           else
             echo "iOS project exists, skipping prebuild"
           fi
-      - name: Cache CocoaPods
-        uses: actions/cache@v4
-        with:
-          path: |
-            apps/llm/ios/Pods
-            ~/Library/Caches/CocoaPods
-            ~/.cocoapods
-          key: ${{ runner.os }}-pods-${{ hashFiles('apps/llm/ios/Podfile.lock') }}
-          restore-keys: |
-            ${{ runner.os }}-pods-
       - name: Install CocoaPods dependencies
         working-directory: apps/llm/ios
         run: |
-          if [ ! -d "Pods" ]; then
-            pod install
-          else
-            echo "Pods directory exists, skipping install"
-          fi
+          pod install
       - name: Build app
         working-directory: apps/llm/ios
         run: |