build: drop sbindir variable

The sbindir variable is provided for free with autotools.  For proper
replacement you must use @sbindir@.

Reference: www.gnu.org/prep/standards/html_node/Directory-Variables.html

Change-Id: I8847256a8ee5178f65427d986eaf54f5ba2bb7e1
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/configure.ac b/configure.ac
index c9a2591..6233aee 100644
--- a/configure.ac
+++ b/configure.ac
@@ -29,8 +29,6 @@
 AC_ARG_VAR(SNOOP_DEVICE, "Path to snoop device")
 AC_ARG_VAR(POST_CODE_BYTES, "Post code byte size")
 AC_ARG_VAR(SYSTEMD_TARGET, "Target for starting this service")
-AC_ARG_VAR(sbindir, "sbin full path")
-AS_IF([test "x$sbindir" == "x"], [sbindir="/usr/sbin"])
 
 PKG_PROG_PKG_CONFIG
 AC_ARG_WITH([systemdsystemunitdir],