Remove value of technical parameters in nhd files

[ChHaeni]

Values of the technical parameters in the nhd files are not used, but read in from a technical.cfg file and many of the values in the nhd files are no longer up to date and add to misunderstanding when going through the nhd files. E.g.:

+a_high
  value = 0.02
  ++units  
    en = -
  ++description
    For milk yield > standard milk yield

+a_low
  value = 0.1
  ++units  
    en = -
  ++description
    For milk yield < standard milk yield

Where both values are taken from the technical.cfg file as 5%, nowadays... Removing the value entry is possible but leads to a message output:

Value of type Any uselessly passed to val()
  in submethod TWEAK at /home/christoph/repos/5_GitHub/agrammon/lib/Agrammon/Model/Technical.pm6 (Agrammon::Model::Technical) line 10
Value of type Any uselessly passed to val()
  in submethod TWEAK at /home/christoph/repos/5_GitHub/agrammon/lib/Agrammon/Model/Technical.pm6 (Agrammon::Model::Technical) line 10