fix: reduce thread contention in DC TableLoader

[baltzell]

Remove unnecessary/ineffective synchronize locks and privatize methods.

The first 3 modified methods are only called once per event and only by the public, synchronized method TableLoader.Fill(IndexedTable ...). Since their sole caller is also synchronized, removing their own synchronized doesn't have any affect on thread contention or safety, just removes unnecessary locking. We can also make them private to help avoid confusion and misuse.

But the last 2, calc_Time and getDeltaTimeBeta, are called externally, later in each event, and maybe many times per event. Note, their locking isn't useful and does nothing to prevent the underlying data from changing during access or even since initialization; it only prevents multiple threads from calling the same reader method simultaneously.