Track and remove 16.0 targeted removals

Milestone Release notes

• Praefect removals got included in: 16.0
• Gitaly removals got included in: 16.1

What is this MR about

Inspect which 16.0 removals are still to be removed and remove the deprecated configs from files/gitlab-cookbooks/package/libraries/deprecations.rb that are targeted to be removed in %16.0.

Config	MR
cgroups_memory_enabled	Stop accepting the old Gitaly config structure (!6866 - merged)
cgroups_memory_limit	Stop accepting the old Gitaly config structure (!6866 - merged)
cgroups_cpu_enabled	Stop accepting the old Gitaly config structure (!6866 - merged)
separate_database_metrics	Stop accepting the old Praefect config structure (!6867 - merged)
gitlab_default_can_create_group	Remove 'gitlab_default_can_create_group' setting (!6819 - merged)
long list of praefect keys	Stop accepting the old Praefect config structure (!6867 - merged)
long list of gitaly keys	Stop accepting the old Gitaly config structure (!6866 - merged)