Reduce utils.Cfg references (#7650)

* app.UpdateConfig method

* test fix

* another test fix

* the config override option as-was is just error prone, remove it for now

* derp

app/command_channel_rename_test.go

@@ -15,7 +15,7 @@ func TestRenameProviderDoCommand(t *testing.T) {
 	args := &model.CommandArgs{
 		T:         func(s string, args ...interface{}) string { return s },
 		ChannelId: th.BasicChannel.Id,
-		Session:   model.Session{UserId: th.BasicUser.Id, TeamMembers: []*model.TeamMember{&model.TeamMember{TeamId: th.BasicTeam.Id, Roles: model.ROLE_TEAM_USER.Id}}},
+		Session:   model.Session{UserId: th.BasicUser.Id, TeamMembers: []*model.TeamMember{{TeamId: th.BasicTeam.Id, Roles: model.ROLE_TEAM_USER.Id}}},
 	}
 
 	// Blank text is a success