how to fetch StageName from Opportunity team

Try below code

trigger PreventOppTeamDeletion on OpportunityTeamMember (before delete) {
    Id profileId = UserInfo.getProfileId();
    String profileName = [SELECT Id, Name from Profile WHERE Id=:profileId].Name;
    set<id> opporuntiyid= new set<id>();
    for(OpportunityTeamMember opt:Trigger.old){
	opporuntiyid.add(opt.OpportunityId) ;
    }
        Map<Id,Opportunity> memberMap = new Map<Id,Opportunity>([SELECT Id, StageName FROM Opportunity where id IN: opporuntiyid]);
    for(OpportunityTeamMember otm : trigger.old){
        if(profileName != ‘System Administrator’ && memberMap.get(otm.OpportunityId).StageName ==‘Closed Won’){
            otm.addError(‘You are not allowed to Delete Opportunity Team Member. Please contact System Administrator.’);
        }
    }
}