meta-phosphor: move all services to multi-user.target

Instead of obmc-standby.target, use multi-user.target.  This can be
accomplished by changing the definition of SYSTEMD_DEFAULT_TARGET first,
however, the explosive approach by removing that variable and
hard-coding multi-user.target provides a single-step.

Note: This patchset represents effectively the wholesale change of all
services in the meta-phosphor layer as well as the targets.  There are
other parts of OpenBMC that leverage the default variable.

Change-Id: I2b3b2274dd6b32d3832d6e768c26b2607f0ce71c
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/recipes-core/systemd/obmc-targets/obmc-power-stop@.target b/recipes-core/systemd/obmc-targets/obmc-power-stop@.target
index f0429d7..fc22eb1 100644
--- a/recipes-core/systemd/obmc-targets/obmc-power-stop@.target
+++ b/recipes-core/systemd/obmc-targets/obmc-power-stop@.target
@@ -2,7 +2,7 @@
 Description=Power%i Off
 Wants=obmc-power-stop-pre@%i.target
 After=obmc-power-stop-pre@%i.target
-Wants={SYSTEMD_DEFAULT_TARGET}
+Wants=multi-user.target
 Conflicts=obmc-chassis-poweron@%i.target
 Conflicts=fsi-disable.service
 RefuseManualStart=yes