The application manager will never reflect Need For Speed as installed since it wasn't installed from a dpkg file or via apt-get, it was just unpacked and executed.

The webOS application files created by the preenv's "desktopgen" script all begin with: "pre"l, so look for that in /usr/share/applications/hildon.

Better yet try this (as root):
cd /usr/share/applications/hildon
grep -i nfsu *

Look for what file comes back as a hit, and delete that .desktop file.

Then you can delete the /home/user/applications/com.ea.... (or whereever you installed it) directory that holds the game data.