Use wl_container_of internally

Rather than have two versions of the macro with slightly different usages,
just use wl_container_of internally.

This also removes use of statement expressions, a GNU C extension.

Signed-off-by: Michael Forney <mforney@mforney.org>
1 job for container-of in 1 minute and 47 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #332019
build-native

00:01:47