tree-wide: warn when sd_notify fails with READY=1 or FDSTOREREMOVE=1

tree-wide: warn when sd_notify fails with READY=1 or FDSTOREREMOVE=1

Most sd_notify() calls are like log_info() — the result is only informative
and if they fail, it's best ignore this. But if a call with READY=1 fails,
the unit may enter a failed state, so we should warn about this. Similarly
for FSTOREREMOVE=1: the manager may be left with a stale fd, at least wasting
resources.