rugnux: always write both MTZ and CIF; drop --scaling-output

The merged reflections were written in one of mtz/cif/txt selected by
--scaling-output. Write both an MTZ and an mmCIF unconditionally instead - each
has its uses downstream (MTZ for the CCP4/phenix tools, mmCIF for deposition) -
and remove the format selector, the plain-text .hkl writer, and the now-unused
IntensityFormat enum / ScalingSettings::FileFormat plumbing.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

common/ScalingSettings.cpp

@@ -212,15 +212,6 @@ double ScalingSettings::GetMinCapturedFraction() const {
     return min_captured_fraction;
 }
 
-ScalingSettings &ScalingSettings::FileFormat(IntensityFormat input) {
-    intensity_format = input;
-    return *this;
-}
-
-IntensityFormat ScalingSettings::GetFileFormat() const {
-    return intensity_format;
-}
-
 ScalingSettings &ScalingSettings::RfreeFraction(double input) {
     if (input < 0.0 || input > 1.0)
         throw JFJochException(JFJochExceptionCategory::InputParameterInvalid, "R-free fraction must be between 0 and 1");