How can I prevent Django from creating an index during the initial migration for CrateDB?

I'm developing a driver for CrateDB, which indexes everything by default and does not support adding a new index after table creation. However, the initial migration (sessions.0001_initial) attempts to run the following command:

PYTHONCopied
CREATE INDEX "django_session_expire_date_a5c62663" ON "django_session" ("expire_date")

I tried to disable index creation by modifying my backend features and schema editor as shown below:

PYTHONCopied
class DatabaseFeatures(BaseDatabaseFeatures):
    # Does the backend support partial indexes (CREATE INDEX ... WHERE ...)?
    supports_partial_indexes = False
    supports_functions_in_partial_indexes = False

    # Does the backend support indexes on expressions?
    supports_expression_indexes = False

PYTHONCopied
class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
    def add_index(self, model, index):
        return ()

    def add_constraint(self, model, constraint):
        return ()

Despite these changes, Django still issues the CREATE INDEX command. How can I stop Django from generating this statement without resorting to hacks like setting sql_create_index = ("select 1")?

Thanks in advance.