magento-engcom/import-export-improvements#44: Update the sample customer csv

[dmanners]

Description

• remove the columns reward_update_notification and reward_warning_notification
• these attributes are no longer valid but have still been in the sample customer.csv
• with this change you can now download the sample customer csv and import it directly without error

Fixed Issues (if relevant)

1. Importing 'Customers Main File' #44: Importing 'Customers Main File'

Manual testing scenarios

1. Go to 'System' > 'Data Transfer' > 'Import'
2. Select 'Customers Main File' as 'Entity Type'
3. Click on 'Download Sample File' link
4. Select the file downloaded to import

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)