Revert "smurf: Fix WVM to CSO calibration"

This reverts commit fe79e5384b647916ebbed2790d5560e0470c1149.

The commit was already partly removed in commit f4f9e062aa but
the remaining part which mangles a WVM tau value read from FITS
headers causes a problem since commit d0c291b6d9 which adjusts
the WVM FITS headers.  I think that WVM to CSO corrections
were being applied twice in this case.