Improve source catalog / tweakreg PSF accuracy

[schlafly]

I inadvertently left a (large!) fudge factor in the requirement testing tweakreg fit accuracy:
https://github.com/spacetelescope/romancal/blob/main/romancal/regtest/test_tweakreg.py#L80
The factor of 100 on this line should be deleted.

When we delete that, we will start failing tests. The astrometric RMS we are getting in tweakreg is not so bad, so it's unclear why there is a large shift. It appears to be almost entirely a constant shift. One possibility is that this came in with an update to WebbPSF; romancal uses new WebbPSF PSFs, while the L1s were generated using older PSFs. We should see what's the ultimate cause of the discrepancy there and remove the spurious factor of 100.