Removed supports_binary_field flag as all backends support them

It was mainly for MySQL on Python 3, but now the current
recommended MySQL driver for Python 3 (mysqlclient) does support
binary fields, it is unneeded. Refs #20377.

django/db/backends/__init__.py

@@ -581,8 +581,6 @@ class BaseDatabaseFeatures(object):
     supports_subqueries_in_group_by = True
     supports_bitwise_or = True
 
-    supports_binary_field = True
-
     # Is there a true datatype for timedeltas?
     has_native_duration_field = False
 

django/db/backends/mysql/base.py

@@ -169,8 +169,6 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     has_select_for_update = True
     has_select_for_update_nowait = False
     supports_forward_references = False
-    # XXX MySQL DB-API drivers currently fail on binary data on Python 3.
-    supports_binary_field = six.PY2
     supports_regex_backreferencing = False
     supports_date_lookup_using_string = False
     can_introspect_autofield = True

tests/migrations/test_operations.py

@@ -7,7 +7,6 @@ try:
 except ImportError:
     sqlparse = None
 
-from django import test
 from django.db import connection, migrations, models, transaction
 from django.db.migrations.migration import Migration
 from django.db.migrations.state import ProjectState
@@ -669,7 +668,6 @@ class OperationTests(OperationTestBase):
         self.assertEqual(pony.digits, "42")
         self.assertEqual(pony.quotes, '"\'"')
 
-    @test.skipUnlessDBFeature('supports_binary_field')
     def test_add_binaryfield(self):
         """
         Tests the AddField operation on TextField/BinaryField.

tests/model_fields/tests.py

@@ -655,7 +655,6 @@ class FileFieldTests(unittest.TestCase):
 class BinaryFieldTests(test.TestCase):
     binary_data = b'\x00\x46\xFE'
 
-    @test.skipUnlessDBFeature('supports_binary_field')
     def test_set_and_retrieve(self):
         data_set = (self.binary_data, six.memoryview(self.binary_data))
         for bdata in data_set:

tests/serializers_regress/tests.py

@@ -450,7 +450,6 @@ class SerializerTests(TestCase):
         self.assertEqual(base_data, proxy_proxy_data.replace('proxy', ''))
 
 
-@skipUnlessDBFeature('supports_binary_field')
 def serializerTest(format, self):
 
     # Create all the objects defined in the test data