remove reference to overlay2 as a filesystem
remove reference to overlay2 as a filesystem

`overlay2` was incorrectly included as a filesystem that the `overlay` and `overlay2` storage drivers can't run on. `overlay2` is the name of the storage driver, but the filesystem is just called `overlay`. It was called `overlayfs` in older versions or the kernel, which would have helped disambiguate this, but I think we should continue to use `overlay` as the name of the filesystem because that's what the kernel uses now.
anweiss/docker.github.io,phiroict/docker,JimGalasyn/docker.github.io,londoncalling/docker.github.io,shin-/docker.github.io,joeuo/docker.github.io,shubheksha/docker.github.io,anweiss/docker.github.io,docker-zh/docker.github.io,docker/docker.github.io,bdwill/docker.github.io,londoncalling/docker.github.io,londoncalling/docker.github.io,johnstep/docker.github.io,joaofnfernandes/docker.github.io,LuisBosquez/docker.github.io,phiroict/docker,joaofnfernandes/docker.github.io,anweiss/docker.github.io,JimGalasyn/docker.github.io,anweiss/docker.github.io,bdwill/docker.github.io,LuisBosquez/docker.github.io,joaofnfernandes/docker.github.io,docker/docker.github.io,johnstep/docker.github.io,LuisBosquez/docker.github.io,bdwill/docker.github.io,joaofnfernandes/docker.github.io,joaofnfernandes/docker.github.io,docker/docker.github.io,docker-zh/docker.github.io,johnstep/docker.github.io,thaJeztah/docker.github.io,shin-/docker.github.io,thaJeztah/docker.github.io,anweiss/docker.github.io,shubheksha/docker.github.io,phiroict/docker,docker-zh/docker.github.io,docker/docker.github.io,shin-/docker.github.io,docker/docker.github.io,bdwill/docker.github.io,shubheksha/docker.github.io,LuisBosquez/docker.github.io,johnstep/docker.github.io,joeuo/docker.github.io,joeuo/docker.github.io,JimGalasyn/docker.github.io,shubheksha/docker.github.io,thaJeztah/docker.github.io,shin-/docker.github.io,londoncalling/docker.github.io,shin-/docker.github.io,joeuo/docker.github.io,docker-zh/docker.github.io,JimGalasyn/docker.github.io,phiroict/docker,LuisBosquez/docker.github.io,thaJeztah/docker.github.io,bdwill/docker.github.io,shubheksha/docker.github.io,phiroict/docker,londoncalling/docker.github.io,JimGalasyn/docker.github.io,johnstep/docker.github.io,docker-zh/docker.github.io,joeuo/docker.github.io,thaJeztah/docker.github.io