mel: for systemd, pull in alsa-states, not alsa-state

alsa-state provides the initscript for sysvinit, but systemd has its own
services to save/load alsa state, so at best the previous behavior was
redundant. Fix that by pulling in just the pre-supplied alsa state files, not
the startup script.

This also works around this build failure:

    - alsa-state inherits update-rc.d, which adds an initscripts-functions runtime
      dependency at package creation time (but not at parse time)
    - For a pure systemd configuration, VIRTUAL-RUNTIME_initscripts is set to the
      empty string, to avoid pulling initscripts into the image
    - As a result, nothing in this configuration pulls 'initscripts' into the
      build, yet the rdepends is still set to it

JIRA: SB-2016

Signed-off-by: Christopher Larson <kergoth@gmail.com>