Restore equivalence between moments and moments_enhanced.

[HannoSpreeuw]

• The equivalent code change for measure.moments to tackle 1) still needs to be implemented; 2) does not seem to be a problem for measure.moments.

• In terms of equivalence between measure.moments and measure.moments_enhanced one may seek an equivalent of forced beam for measure.moments.

Originally posted by @HannoSpreeuw in #187 (comment)

[HannoSpreeuw]

  [ ]  In terms of equivalence between `measure.moments` and `measure.moments_enhanced` one may seek an equivalent of `forced beam` for `measure.moments`.

After consideration, this does not seem to apply, since we have this condition in the extract module:

        if not fixed:
            # Moments can only be computed if no parameters are fixed.
            try:
                param.update(
                    measure.moments(
                        data,
                        fudge_max_pix_factor,
                        beam,
                        beamsize,
                        moments_threshold,
                    )
                )

This means that measure.moments will never be run for forced beams, contrary to measure.moments_enhanced, which is applied vectorized and is not used to produce initial values for Gaussian fits.
Of course, one could change that if not fixed conditional, but that is beyond the scope of this issue. I will tick the box to indicate that this does not apply.