remove deprecated goto_instructiont::get_function_call

[kroening]

The method is deprecated; the commit includes some refactoring to enable the
removal of the final set of users.

• Each commit message has a non-empty body, explaining why the change was made.
• n/a Methods or procedures I have added are documented, following the guidelines provided in CODING_STANDARD.md.
• 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).
• My PR is restricted to a single feature or bugfix.
• n/a White-space or formatting changes outside the feature-related changed lines are in commits of their own.

[codecov]

Codecov Report

Merging #6391 (a375eff) into develop (ea13baf) will increase coverage by 0.00%.
The diff coverage is 89.57%.

@@           Coverage Diff            @@
##           develop    #6391   +/-   ##
========================================
  Coverage    75.97%   75.97%           
========================================
  Files         1523     1523           
  Lines       164194   164191    -3     
========================================
- Hits        124750   124749    -1     
+ Misses       39444    39442    -2     

Impacted Files	Coverage Δ
src/goto-instrument/contracts/contracts.h	100.00% <ø> (ø)
src/goto-instrument/dot.cpp	0.00% <0.00%> (ø)
src/goto-programs/goto_program.h	90.49% <ø> (+0.43%)	⬆️
src/solvers/smt2_incremental/smt_responses.h	0.00% <0.00%> (ø)
...rc/solvers/smt2_incremental/smt_solver_process.cpp	25.00% <25.00%> (ø)
src/goto-symex/symex_main.cpp	86.00% <60.00%> (+0.03%)	⬆️
src/goto-checker/solver_factory.cpp	76.49% <66.66%> (ø)
src/solvers/smt2_incremental/smt_solver_process.h	66.66% <66.66%> (ø)
src/goto-analyzer/taint_analysis.cpp	78.21% <75.00%> (-0.22%)	⬇️
src/goto-analyzer/static_simplifier.cpp	87.34% <83.33%> (+0.16%)	⬆️
... and 22 more

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