Drop Python 3.7 handling for pickle protocol 4 (#12857)

Fixes #12851

Now that Python 3.8 is the minimum supported version, drop the special casing for Python 3.7's `HIGHEST_PROTOCOL`, which was 4 (not 5). In Python 3.8+, `HIGHEST_PROTOCOL >= 5`. So none of these branches are needed any more.

Authors:
  - https://github.com/jakirkham
  - GALI PREM SAGAR (https://github.com/galipremsagar)
  - Ashwin Srinath (https://github.com/shwina)

Approvers:
  - GALI PREM SAGAR (https://github.com/galipremsagar)
  - Bradley Dice (https://github.com/bdice)

URL: #12857

python/cudf/cudf/tests/test_pack.py

@@ -191,15 +191,14 @@ def check_packed_pickled_equality(df):
     assert isinstance(sortvaldf.index, GenericIndex)
     assert_packed_frame_picklable(sortvaldf)
     # out-of-band
-    if pickle.HIGHEST_PROTOCOL >= 5:
-        buffers = []
-        serialbytes = pickle.dumps(
-            pack(df), protocol=5, buffer_callback=buffers.append
-        )
-        for b in buffers:
-            assert isinstance(b, pickle.PickleBuffer)
-        loaded = unpack(pickle.loads(serialbytes, buffers=buffers))
-        assert_eq(loaded, df)
+    buffers = []
+    serialbytes = pickle.dumps(
+        pack(df), protocol=5, buffer_callback=buffers.append
+    )
+    for b in buffers:
+        assert isinstance(b, pickle.PickleBuffer)
+    loaded = unpack(pickle.loads(serialbytes, buffers=buffers))
+    assert_eq(loaded, df)
 
 
 def assert_packed_frame_picklable(df):

python/cudf/cudf/tests/test_pickling.py

@@ -1,4 +1,4 @@
-# Copyright (c) 2018-2022, NVIDIA CORPORATION.
+# Copyright (c) 2018-2023, NVIDIA CORPORATION.
 
 import pickle
 
@@ -25,15 +25,12 @@ def check_serialization(df):
     assert isinstance(sortvaldf.index, (GenericIndex, RangeIndex))
     assert_frame_picklable(sortvaldf)
     # out-of-band
-    if pickle.HIGHEST_PROTOCOL >= 5:
-        buffers = []
-        serialbytes = pickle.dumps(
-            df, protocol=5, buffer_callback=buffers.append
-        )
-        for b in buffers:
-            assert isinstance(b, pickle.PickleBuffer)
-        loaded = pickle.loads(serialbytes, buffers=buffers)
-        assert_eq(loaded, df)
+    buffers = []
+    serialbytes = pickle.dumps(df, protocol=5, buffer_callback=buffers.append)
+    for b in buffers:
+        assert isinstance(b, pickle.PickleBuffer)
+    loaded = pickle.loads(serialbytes, buffers=buffers)
+    assert_eq(loaded, df)
 
 
 def assert_frame_picklable(df):