[m-rev.] diff: remove the condition field from items

[Zoltan Somogyi]

We used to have a condition field in pred_infos, but we deleted it in 2004,
saying "it won't be used in its current form". The parser that was supposed
to read in conditions has never been written, and this field has been sitting
there unused in several kinds of items for the last 20 years. These fields
also won't be used in their current form, and they gave me unnecessary work
to do when factoring out the common code for aux preds for mutables, so
I am deleting them to prevent another such occurrence.

Zoltan.
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