Remove use of mapper call

Replace invocations of mapper call with a call to busctl and mapper
get-service.  This provides equivalent functionality but opens the
door for dropping a systemd patch we have carried for some time.

Change-Id: Iea0cce89341939b49b095d1f5010415578331d4d
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/common/recipes-phosphor/leds/phosphor-led-manager/obmc-led-group-start@.service b/common/recipes-phosphor/leds/phosphor-led-manager/obmc-led-group-start@.service
index 38d6c5a..e0e1fc9 100644
--- a/common/recipes-phosphor/leds/phosphor-led-manager/obmc-led-group-start@.service
+++ b/common/recipes-phosphor/leds/phosphor-led-manager/obmc-led-group-start@.service
@@ -8,5 +8,5 @@
 Type=oneshot
 RemainAfterExit=yes
 Restart=no
-ExecStart=/usr/bin/env mapper call /xyz/openbmc_project/led/groups/%i org.freedesktop.DBus.Properties Set ssv xyz.openbmc_project.Led.Group Asserted b true
-SyslogIdentifier=mapper
+ExecStart=/bin/sh -c "busctl call `mapper get-service /xyz/openbmc_project/led/groups/%i` /xyz/openbmc_project/led/groups/%i org.freedesktop.DBus.Properties Set ssv xyz.openbmc_project.Led.Group Asserted b true"
+SyslogIdentifier=obmc-led-group-start