Revert "feat: support type alias (go-gorm#90)"

This reverts commit ff88afd.

migrator.go

@@ -26,11 +26,6 @@ ORDER BY
 	INDEX_NAME,
 	SEQ_IN_INDEX`
 
-var typeAliasMap = map[string][]string{
-	"bool":    {"tinyint"},
-	"tinyint": {"bool"},
-}
-
 type Migrator struct {
 	migrator.Migrator
 	Dialector
@@ -325,7 +320,3 @@ func (m Migrator) CurrentSchema(stmt *gorm.Statement, table string) (string, str
 
 	return m.CurrentDatabase(), table
 }
-
-func (m Migrator) GetTypeAliases(databaseTypeName string) []string {
-	return typeAliasMap[databaseTypeName]
-}