Remove not needed local variable

Signed-off-by: Michal Čihař <michal@cihar.com>

weblate/trans/models/unit.py

@@ -864,14 +864,14 @@ class Unit(models.Model):
         if len(checks_to_run) == 0:
             return
 
-        checks = self.checks()
-
         src = self.get_source_plurals()
         tgt = self.get_target_plurals()
-        old_target_checks = set(checks.values_list('check', flat=True))
-        old_source_checks = set(self.source_checks().values_list(
-            'check', flat=True
-        ))
+        old_target_checks = set(
+            self.checks().values_list('check', flat=True)
+        )
+        old_source_checks = set(
+            self.source_checks().values_list('check', flat=True)
+        )
 
         # Run all checks
         for check in checks_to_run: