opam: 2.x no longer needs remove:, use os-family

[Martin Lucina]

Reminder to self to do this for the opam files here, and while we're at it we can probably remove the related Makefile targets.

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Would it be ok to remove the remove fields and change it in the source repository? Since opam 2.0 they are not necessary unless it is to remove a configuration file or something that has been created after installation.

Also,

["linux-libc-dev"] {os-distribution = "debian"}
["linux-libc-dev"] {os-distribution = "ubuntu"}

can be reduced to:

["linux-libc-dev"] {os-family = "debian"}

Could you also change this? This would allow to handle Raspbian and similar derived distributions.

Originally posted by @kit-ty-kate in ocaml/opam-repository#16443 (comment)