Assert no read barriers for method maps in JIT.

Add a TODO for `JitCodeCache::GetProfiledMethods()` where
we seem to be using read barriers for potentially dead
methods in `profiling_infos_`.

Also add TODOs for cleaning `jni_stubs_map_` for transition
to debuggable.

Test: m test-art-host-gtest
Test: testrunnr.py --host --jit
Change-Id: Idb6cb51a677754ed187d53319ba5bb2b1cb8e33b