fix(dark-mode-button): delete the duplicated dark mode button (#735)

## Description:

Fix the overlapping dark mode button. It happened because there was a
duplicate in the index.html

Linked issue: https://github.com/openfrontio/OpenFrontIO/issues/659

I tested in game + mobile to find out if there was no reason for this
duplicate. I'm not 100% familiar with the project so feel free to double
check 🙏

## Media

Before:


https://github.com/user-attachments/assets/09ab3449-1503-4da0-84d9-e0d1fa61507b

After:


https://github.com/user-attachments/assets/0c0ef2ad-5071-4030-baa9-a9fb85edd1e9

## Please complete the following:

- [x] I have added screenshots for all UI updates
- [x] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced
- [x] I understand that submitting code with bugs that could have been
caught through manual testing blocks releases and new features for all
contributors

## Please put your Discord username so you can be contacted if a bug or
regression is found:

Nilsfram

src/client/index.html

@@ -242,7 +242,6 @@
       </div>
     </div>
 
-    <dark-mode-button></dark-mode-button>
     <!-- Main container with responsive padding -->
     <main class="flex justify-center flex-grow">
       <div class="container pt-12">