ash: fix unset in standalone mode

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/shell/ash_test/ash-standalone/var_standalone1.tests b/shell/ash_test/ash-standalone/var_standalone1.tests
new file mode 100755
index 0000000..1e905ba
--- /dev/null
+++ b/shell/ash_test/ash-standalone/var_standalone1.tests
@@ -0,0 +1,2 @@
+VAR=42 $THIS_SH -c 'unset VAR; env | grep ^VAR'
+echo Done: $?