Dockerfile: remove libdevmapper-dev

The devicemapper graphdriver has been removed in commit
dc11d2a2d8, and we should
no longer need this.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

Dockerfile.simple

@@ -26,7 +26,6 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
 		cmake \
 		git \
 		libapparmor-dev \
-		libdevmapper-dev \
 		libseccomp-dev \
 		ca-certificates \
 		e2fsprogs \