fsmonitor: use nonnormalset from dirstatemap `dirstate._nonnormalset` has been moved to `dirstate._map.nonnormalset` by 60927b19ed65 (dirstate: move nonnormal and otherparent sets to dirstatemap) and is guaranteed to be existed. Let's update fsmonitor code to use the new `nonnormalset`. Thix fixed a perf regression that slows down `hg status` by 0.5 seconds in one of our production repos. Differential Revision: https://phab.mercurial-scm.org/D1184