Make atexit.dlclose work for glibc

* build libtest_atexit.so
 * remove atexit(NULL) - glibc segfaults on it

Bug: 15350494
Change-Id: I27d79130c32c5691b0e8790a57d92f9710f5bf4a

tests/atexit_testlib.cpp

@@ -71,6 +71,5 @@ extern "C" void register_atexit(std::string* sequence, bool* valid_this_in_stati
   atexit_valid_this_in_static_dtor = valid_this_in_static_dtor;
   atexit(atexit_handler_regular);
   atexit(atexit_handler_with_atexit);
-  atexit(NULL);
 }