Fix memory-leak on soinfo_free()

Bug: http://b/22290728
Change-Id: I00747056db2cd3ff8b33936278464daed7236536
(cherry picked from commit 609f11b31e)

linker/linker.cpp

@@ -277,6 +277,7 @@ static void soinfo_free(soinfo* si) {
     sonext = prev;
   }
 
+  si->~soinfo();
   g_soinfo_allocator.free(si);
 }