Previously, second mkIf for cleanup case took precedence when merge with
`//`. Now it's 2 modules: one for selfprivacy.modules.nextcloud.enable
== true, another for selfprivacy.modules.nextcloud.enable == false.
Now it should work for all nested imports too. `imports` are traversed
recursively to redefine each imported module function with altered one,
constraining its config attribute (respecting config-paths-needed.json).