Revert "fix: create index failed without err (#282)" (#284)

This reverts commit f300cc4.

migrator.go

@@ -146,14 +146,7 @@ func (m Migrator) CreateIndex(value interface{}, name string) error {
  createIndexSQL += " WHERE " + idx.Where
  }
 
- err := m.DB.Exec(createIndexSQL, values...).Error
- if err != nil {
- return err
- }
-
- if !m.HasIndex(value, name) {
- return fmt.Errorf("failed to create index with name %v", name)
- }
+ return m.DB.Exec(createIndexSQL, values...).Error
  }
  }