If it was set via GPO it would go away once the system was removed from the domain. If done via GPP the only way is to manually remove registry settings set by said GPP. Also GPOs can be set locally via gpedit.msc anything set in here specifically on the machine will persist after removal from a domain. These you can launch
gpedit.msc
Expand 'Administrative Templates' and look at both User and Computer 'All Settings' and sort by state. If anything is not set to 'Not configured' then you have settings enforced and you need to click each one and change them to 'Not configured'. Reboot after changing settings.