I recently ran in to a problem where i wanted to perform a clean configuration of one of my ESXi hosts from an NSX perspective, however i ran in to a problem where NSX was reporting that the packages are already installed. To fix the issue i had to run the following to list the packages installed:
esxcli software vib list | grep -i nsx
Once i had the list all i had to do is uninstall them using:
esxcli software vib remove -n packagename1 -n packagename2 ...
Once the uninstall was complete i was able to redeploy NSX from the NSX Manager