Removed deprecated functions and modules from airflow.www module.

• Config flag default warning cookie_samesite option in section [webserver] removed.
• Legacy decorator @has_access in airflow.www.auth: Please use one of the decorator has_access_* defined in airflow/www/auth.py instead.
• Removed legacy modules airflow.www.security: Should be inherited from airflow.providers.fab.auth_manager.security_manager.override.FabAirflowSecurityManagerOverride instead. The constant value EXISTING_ROLES should be used from airflow.www.security_manager module.
• Removed the method get_sensitive_variables_fields() from airflow.www.utils: Please use airflow.utils.log.secrets_masker.get_sensitive_variables_fields instead.
• Removed the method should_hide_value_for_key() from airflow.www.utils: Please use airflow.utils.log.secrets_masker.should_hide_value_for_key instead.