opkg-keyrings: do not use 'exit 1' to postpone to first boot

Since `229f4e9 package.bbclass: add support for
pkg_postinst_ontarget()' applied in oe-core, use
pkg_postinst_ontarget to run postinst at first boot.

(From OE-Core rev: a6e62aae8f83696755828631e5ff67a579a6462f)

Signed-off-by: Hongxu Jia <hongxu.jia@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-devtools/opkg/opkg-keyrings_1.0.bb

@@ -35,14 +35,6 @@ FILES_${PN} = "${datadir}/opkg/keyrings"
 # We need 'opkg-key' to run the postinst script
 RDEPENDS_${PN} = "opkg"
 
-pkg_postinst_${PN} () {
-#! /bin/sh
-set -e
-
-if [ x"$D" = "x" ]; then
-    # On target
-    opkg-key populate
-else
-    exit 1
-fi
+pkg_postinst_ontarget_${PN} () {
+opkg-key populate
 }