Remove unnecessary SystemRandom from SQLBaseStore (#9987)

It's not obvious that instances of SQLBaseStore each need their own
instances of random.SystemRandom(); let's just use random directly.

Introduced by 5283988

Signed-off-by: Dan Callahan <danc@element.io>

changelog.d/9987.misc

@@ -0,0 +1 @@
+Remove unnecessary property from SQLBaseStore.

synapse/storage/_base.py

@@ -14,7 +14,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 import logging
-import random
 from abc import ABCMeta
 from typing import TYPE_CHECKING, Any, Collection, Iterable, Optional, Union
 
@@ -44,7 +43,6 @@ def __init__(self, database: DatabasePool, db_conn: Connection, hs: "HomeServer"
         self._clock = hs.get_clock()
         self.database_engine = database.engine
         self.db_pool = database
-        self.rand = random.SystemRandom()
 
     def process_replication_rows(
         self,

synapse/storage/databases/main/registration.py

@@ -14,6 +14,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 import logging
+import random
 import re
 from typing import TYPE_CHECKING, Any, Dict, List, Optional, Tuple, Union
 
@@ -997,7 +998,7 @@ def set_expiration_date_for_user_txn(self, txn, user_id, use_delta=False):
         expiration_ts = now_ms + self._account_validity_period
 
         if use_delta:
-            expiration_ts = self.rand.randrange(
+            expiration_ts = random.randrange(
                 expiration_ts - self._account_validity_startup_job_max_delta,
                 expiration_ts,
             )