Remove typecheckt interface from linkingt

[tautschnig]

There is no particular benefit in this inheritance. Also prepare for maintaining state across multiple calls to the linker by making the source symbol table an argument specific to each linking call.

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• n/a The feature or user visible behaviour I have added or modified has been documented in the User Guide in doc/cprover-manual/
• Regression or unit tests are included, or existing tests cover the modified code (in this case I have detailed which ones those are in the commit message).
• n/a My commit message includes data points confirming performance improvements (if claimed).
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[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: -0.03 ⚠️

Comparison is base (cfcfcf6) 78.57% compared to head (7df3543) 78.55%.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #7728      +/-   ##
===========================================
- Coverage    78.57%   78.55%   -0.03%     
===========================================
  Files         1685     1685              
  Lines       192962   192966       +4     
===========================================
- Hits        151624   151579      -45     
- Misses       41338    41387      +49     

Impacted Files	Coverage Δ
src/goto-programs/link_goto_model.cpp	87.50% <100.00%> (ø)
src/linking/linking.cpp	62.13% <100.00%> (-7.16%)	⬇️
src/linking/linking_class.h	100.00% <100.00%> (ø)

... and 1 file with indirect coverage changes

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