[Bug](decimalv3) always use decimalv3 for show create table (#16295)

fe/fe-common/src/main/java/org/apache/doris/catalog/ScalarType.java

@@ -564,7 +564,7 @@ public class ScalarType extends Type {
             case DECIMAL32:
             case DECIMAL64:
             case DECIMAL128:
-                String typeName = Config.enable_decimal_conversion ? "decimal" : "decimalv3";
+                String typeName = "decimalv3";
                 if (Strings.isNullOrEmpty(precisionStr)) {
                     stringBuilder.append(typeName).append("(").append(precision)
                         .append(", ").append(scale).append(")");