Use std::shared_ptr in Epoll's callback list. am: 2cf268ab9f am: 5e66f7148b am: 6fa3c6a94a am: 5ca4715fcd

Original change: https://googleplex-android-review.googlesource.com/c/platform/system/core/+/15128087

Change-Id: I548e1a74906071703007415a73345f02b550f354