chore: remove entity index again

chore: add migration note

repositories/heartbeat.go

@@ -1,7 +1,6 @@
 package repositories
 
 import (
-	"errors"
 	"github.com/muety/wakapi/models"
 	"gorm.io/gorm"
 	"gorm.io/gorm/clause"
@@ -158,16 +157,10 @@ func (r *HeartbeatRepository) CountByUsers(users []*models.User) ([]*models.Coun
 }
 
 func (r HeartbeatRepository) GetEntitySetByUser(entityType uint8, user *models.User) ([]string, error) {
-	columns := []string{"project", "language", "editor", "operating_system", "machine"}
-	if int(entityType) >= len(columns) {
-		// invalid entity type
-		return nil, errors.New("invalid entity type")
-	}
-
 	var results []string
 	if err := r.db.
 		Model(&models.Heartbeat{}).
-		Distinct(columns[entityType]).
+		Distinct(models.GetEntityColumn(entityType)).
 		Where(&models.Heartbeat{UserID: user.ID}).
 		Find(&results).Error; err != nil {
 		return nil, err