You can safely uninstall virtualmin-lamp-stack, as long as you don’t ever run apt-get autoremove (or as long as you use apt-get install ... for all of the packages so they get marked as installed manually, so they won’t get autoremoved when the package that depends on them goes away). This package is just a list of dependencies. Now that your system is installed, you don’t really need the package anymore.
But, really, seriously, if you ever use autoremove without noticing that the entire Virtualmin stack will be removed, it’ll completely slaughter your system.