fix: if a data model field binding is removed, delete the prop

[lassopicasso]

Description

If removed, set the data model field as undefined.

Related Issue(s)

• Removing a data model binding should delete the entire node #14296

Verification

• Your code builds clean without any errors or warnings
• Manual testing done (required)
• Relevant automated test added (if you find this hard, leave it and we'll help out)

Documentation

• User documentation is updated with a separate linked PR in altinn-studio-docs. (if applicable)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.52%. Comparing base (8783861) to head (d69792f).
Report is 8 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #14297   +/-   ##
=======================================
  Coverage   95.52%   95.52%           
=======================================
  Files        1831     1831           
  Lines       23785    23790    +5     
  Branches     2755     2757    +2     
=======================================
+ Hits        22720    22725    +5     
  Misses        807      807           
  Partials      258      258           

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[lassopicasso]

Great work @mlqn ! The code handles a complicated case, and is solid! As we talked about, prob add a test when the value is undefined or null.
I would have approved this, but github won't let me :D