Clean up the Virtualmin package

[iliajie]

Hey Jamie,

As discussed here #998 (comment), we should not be shipping packages and mention options that have been obsolete for 15–20 years as it doesn’t leave a good impression, especially when trying to attract new users.

Therefore, I suggest we drop all code related to Ensim, LXAdmin, including removing PHP/Serialization.pm.

And, S3 modules can now be remove as well, as discussed in the same ticket here #998 (comment).

[jcameron]

I'm OK with dropping LXadmin and Ensim support since it looks like those control panels are long gone.

And also PHP/Serialization since it's only used by the LXadmin migration code.

Please send me a PR for these!

[iliajie]

Thanks! I will, in a bit!

[shoulders]

Linking to this issue just incase it is of any use. Removal of these admin panels were requested here + others.

#872 Remove Legacy migrate backup file types