Just delete that .dll from the SKSE/Plugin path in your SSE folder. It's wrongly been packaged into the archive repeatedly, and it has become something like a running gag that Pfiffy forgets to NOT package it again when he next updates the conversion. 😜 So - nothing wrong with your install.
However, you could have found that by reading the recent thread pages, because this questions pops up more often than draugr in a nordic ruin. That's also why MMG has become a tad grumpy whenever the setvehiclefixedplugin.dll-question reincarnates here AGAIN.