You cannot remove security using the native Actions tools in Acrobat XI Pro, that feature was removed. You can however re-use an Acrobat X Pro sequence file which does it.
Provided all your PDFs have the same password:
You won't be able to edit the Action from within Acrobat, but if you're curious about what it's doing, open it in a text editor.
I tried this and it worked fine until I restarted Acrobat, then the action was gone. I can't reinstall it either, the filename still exists in a directory preventing me from adding the action back. Is there no other way to batch process removing security from PDFs from Acrobat XI forward?