fix: remove index.html from 8-review image

The index.html test/validity file shows up when source code mounts are
done into the /app directory, which makes them show up for anyone that
would use this container image as the base layer of a devcontainer.
Can lead to accidental commits.

Dockerfile.php8-review

@@ -25,4 +25,8 @@ RUN composer global require icanhazstring/composer-unused \
 
 RUN apt-get update && apt-get install -y python3-pip && python3 -m pip install yamllint --break-system-packages
 
+# Caused the appearance of a git untracked index.html file within the GitHub codespace (when image used as
+# the base of a devcontainer)
+RUN rm /app/index.html
+
 ENTRYPOINT ["apache2-foreground"]