Fix phpdbg symlink setup

[ohmyfelix]

Summary

• remove manual /usr/bin/phpdbg symlink creation from all PHP Dockerfiles
• rely on phpdbg package alternatives, which now create the generic phpdbg command

Verification

• inspected failing job log: /usr/bin/phpdbg already exists after installing php8.5-phpdbg
• confirmed no Dockerfile still creates /usr/bin/phpdbg manually
• local Docker build could not be run because the Docker daemon is unavailable in this workspace