Remove AFA implementation

[Adda0]

This PR removes the current implementation of AFA from Mata, as agreed upon in our meetings.

The parsing of AFA .mata files into AFA intermediate format was left untouched. This can be reused for the planned new implementation of AFA. The function to construct Afa from the intermediate AFA was, however, removed.

[codecov]

Codecov Report

Patch coverage has no change and project coverage change: -1.40% ⚠️

Comparison is base (7f18cca) 72.93% compared to head (f7e8a86) 71.54%.
Report is 10 commits behind head on devel.

Additional details and impacted files

@@            Coverage Diff             @@
##            devel     #337      +/-   ##
==========================================
- Coverage   72.93%   71.54%   -1.40%     
==========================================
  Files          33       30       -3     
  Lines        4134     3570     -564     
  Branches      952      830     -122     
==========================================
- Hits         3015     2554     -461     
+ Misses        740      730      -10     
+ Partials      379      286      -93     

see 7 files with indirect coverage changes

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