Allow unused imports in parquet test_common

Can drop this after rebase on commit 80a6ef7 "Fix parquet clippy lints (apache#1254) (apache#2377)", first released in 21.0.0

Author: mcheshkov

parquet/src/util/test_common/mod.rs

@@ -15,6 +15,8 @@
 // specific language governing permissions and limitations
 // under the License.
 
+#![allow(unused)]
+
 pub mod file_util;
 pub mod page_util;
 pub mod rand_gen;