Você pode removê-los, mas não há uma razão strong para isso, pois todos estão desativados. A documentação sobre essas contas pode ser encontrada no arquivo local /usr/share/doc/base-passwd/users-and-groups.html . Muitos pacotes dependem dessas contas existentes e, se algum software exigir uma dessas contas, o pacote recém-adicionado falhará.
O Debian chama essas contas estáticas globais.
The Debian base-passwd package contains the master versions of /etc/passwd and /etc/group. The update-passwd tool keeps the entries in these master files in sync on all Debian systems. They comprise only "global static" ids: that is, those which are reserved globally for the benefit of packages which need to include files owned by those users or groups, or need the ids compiled into binaries. Since this reservation is a serious restriction, these ids must be allocated by the base-passwd maintainer on request. In general, packages should avoid requesting such ids where possible and instead allocate system users or groups dynamically. See Debian Policy for further details.