Remove GAP 4.2 compatibility code

[codecov[bot]]

Codecov Report

Merging #61 (6639556) into master (10ebb5f) will increase coverage by 34.51%. The diff coverage is n/a.

@@             Coverage Diff             @@
##           master      #61       +/-   ##
===========================================
+ Coverage   16.63%   51.15%   +34.51%     
===========================================
  Files         147      147               
  Lines       12861    12862        +1     
  Branches     1940     1922       -18     
===========================================
+ Hits         2140     6580     +4440     
+ Misses      10713     5862     -4851     
- Partials        8      420      +412     

Impacted Files	Coverage Δ
src/GAP_link_via_file.c	69.04% <ø> (+69.04%)	:arrow_up:
src/interactive_pga.c	3.52% <0.00%> (+3.52%)	:arrow_up:
src/text.c	7.14% <0.00%> (+7.14%)	:arrow_up:
src/next_class.c	14.41% <0.00%> (+14.41%)	:arrow_up:
src/interactive_pq.c	15.14% <0.00%> (+15.14%)	:arrow_up:
src/pquotient.c	15.21% <0.00%> (+15.21%)	:arrow_up:
src/AllocateSpace.c	22.77% <0.00%> (+22.77%)	:arrow_up:
src/delete_tables.c	24.13% <0.00%> (+24.13%)	:arrow_up:
src/CloseFile.c	25.00% <0.00%> (+25.00%)	:arrow_up:
src/is_space_exhausted.c	27.27% <0.00%> (+27.27%)	:arrow_up:
... and 79 more