Revert "Always mount a /run tmpfs in the container"

This reverts commit 905795ece624675abe2ec2622b0bbafdb9d7f44c.

FIxes #5973
Closes #5974

This makes sense on a desktop system because at boot, we have init scripts and other nice things that do `mkdir` inside /run for all the directories our silly services might need.  For Docker, we're basically just deleting everything in /run every time we start a new container (which amounts to every RUN line in a Dockerfile too), so this basically just means we'd need wrapper scripts around every command we run to make sure the directories we require to be available in /run are there already.