SCUBA2: make default radius 30 arcsec

Since the standard SCUBA-2 ARCSEC FCFs are quoted for an aperture
radiu of 30 arcsec, it makes sense to have this value as the default
radius for all primitives performing aperture photometry.
PICARD: delete superceded primitive

This primitive was written for the early version of the old
SCUBA2_FCFNEFD recipe. With that recipe having been superceded, this
primitive is no longer necessary, and its functionality is present in
_SCUBA2_PHOTOM_.