Delay model generation: use a distilled version of the ASAP7 Liberty file for faster processing.

When characterizing the ASAP7 process node, the automated timing characterization synthesis runs spend a majority of the runtime reading in the ASAP7 Liberty file.

An experiment was performed by writing a script that removed the `output_current_*`, `internal_power`, and `leakage_power` fields from the ASAP7 Liberty file. This caused synthesis runtime to drop from 8.3s to 1.5s.

If we perform this timing characterization regularly, it would be worth integrating this potential speedup, either by pre-processing the Liberty file to make it smaller, or by using an "NLDM" version of the Liberty file.