trivial: remove support of django-tenant-schemas w/o TenantStorageMixin (#63725)

hobo/multitenant/storage.py

@@ -6,14 +6,7 @@ from django.core.files import File
 from django.core.files.storage import FileSystemStorage
 from django.db import connection
 from django.utils._os import safe_join
-
-try:
-    from tenant_schemas.storage import TenantStorageMixin
-except ImportError:
-
-    class TenantStorageMixin:
-        pass
-
+from tenant_schemas.storage import TenantStorageMixin
 
 __all__ = ('TenantFileSystemStorage',)