Adobe will happily remove that watermark from your component for a small price.
I have Adobe Flex Builder Professional licesne.. Still do I need to pay the money ? Please let me know the more details.
How are you building the app?
I've you've got a Pro license, you should be ok if you are building via FB.
If you are using something like ANT, you'll need to add the license key into the Flex-config.xml in your SDK.