[1pnc] Remove delp from default output

delp is not generally a useful output in particular since -1e5 is hard-coded as offset.
In case of small pressure changes this output also suffers from possible large rounding errors
since p is the primary variables and -1e5 might result in 5 insifgnificant digits.

No other model has this default output field. Hence, this makes
output more consistent across models.
5 jobs for !3144 with cleanup/1pnc-remove-delp-from-default-output
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