rild: Destroy the minijail struct after dropping privs.

This fixes a small memory leak.

Bug: 28178548
Change-Id: Ib97ba3c6a4ee0cd6bed19abef386c1dd3071f518
diff --git a/rild/rild.c b/rild/rild.c
index 53852b8..a55d69b 100644
--- a/rild/rild.c
+++ b/rild/rild.c
@@ -111,6 +111,7 @@
                          CAP_MASK_LONG(CAP_NET_RAW));
 
     minijail_enter(j);
+    minijail_destroy(j);
 
     /*
      * Debuggable build only: