Manual override of uttid leads to non-unique values

[JeltevanBoheemen]

On reading CHAT files, uttid is replaced by the value of either %xsid or %xuid tiers.
This was implemented for SASTA, which relied heavily on xsid values.
However, this replacement causes double uttid values in cases where provided xsid is within range of minimum and maximum uttids. E.g. two sentences with uttid=1 and uttid=2, xsid=1 will lead to double uttid=1.
As SASTA no longer relies on overridden uttid, I suggest removing this mechanic.