Hello,
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Since SEP 12.1 RU1 MP1 and above, there is a new feature added in SEPM itself called as "Third Party Product Removal Feature", check these Articles:
http://www.symantec.com/docs/TECH178757
http://www.symantec.com/docs/TECH195029
In case you would like to have a seperate tool to uninstall SEP or other competitive products, you can try SEPprep.
SEPprep is a unsupported tool that is designed to uninstall any competitive product automatically. This tool can also launch another application before or after removing all competitive products. Therefore you can configure this tool to first remove all competitive products (including Norton products) and then launch the SEP installer automatically and silently.
Check this Article:
http://www.symantec.com/docs/TECH148513
Hope that helps!!