magento-engcom#44: Update the sample customer csv file

 - 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 - these attributes are no longer valid but have still been in the sample customer.csv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

app/code/Magento/ImportExport/Files/Sample/customer.csv

@@ -1,2 +1,2 @@
-email,_website,_store,confirmation,created_at,created_in,disable_auto_group_change,dob,firstname,gender,group_id,lastname,middlename,password_hash,prefix,reward_update_notification,reward_warning_notification,rp_token,rp_token_created_at,store_id,suffix,taxvat,updated_at,website_id,password
-jondoe@example.com,base,default,,"2015-10-30 12:49:47","Default Store View",0,,Jon,,1,Doe,,d708be3fe0fe0120840e8b13c8faae97424252c6374227ff59c05814f1aecd79:mgLqkqgTwLPLlCljzvF8hp67fNOOvOZb:1,,,,07e71459c137f4da15292134ff459cba,"2015-10-30 12:49:48",1,,,"2015-10-30 12:49:48",1,
+email,_website,_store,confirmation,created_at,created_in,disable_auto_group_change,dob,firstname,gender,group_id,lastname,middlename,password_hash,prefix,rp_token,rp_token_created_at,store_id,suffix,taxvat,updated_at,website_id,password
+jondoe@example.com,base,default,,10/30/2015 12:49,Default Store View,0,,Jon,,1,Doe,,d708be3fe0fe0120840e8b13c8faae97424252c6374227ff59c05814f1aecd79:mgLqkqgTwLPLlCljzvF8hp67fNOOvOZb:1,,07e71459c137f4da15292134ff459cba,10/30/2015 12:49,1,,,10/30/2015 12:49,1,