goto-diff: Remove processing of unsupported options

[tautschnig]

The options 1) tested for by the code, 2) documented in --help output,
and 3) actually supported in the cmdlinet configuration were
inconsistent. All supported options are now documented in the --help
output, and testing-for of unsupported options has been removed.

Also, a missing call to goto_functions.update() has been added.

• 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.
• 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 #6512 (3d8b0cd) into develop (21a6267) will increase coverage by 0.00%.
The diff coverage is 42.46%.

@@           Coverage Diff            @@
##           develop    #6512   +/-   ##
========================================
  Coverage    76.10%   76.10%           
========================================
  Files         1548     1548           
  Lines       166326   166301   -25     
========================================
- Hits        126576   126561   -15     
+ Misses       39750    39740   -10     

Impacted Files	Coverage Δ
src/goto-diff/goto_diff_parse_options.cpp	58.02% <0.00%> (-1.03%)	⬇️
src/goto-diff/goto_diff_parse_options.h	100.00% <ø> (ø)
src/goto-instrument/function_assigns.cpp	0.00% <0.00%> (ø)
src/goto-instrument/function_assigns.h	0.00% <0.00%> (ø)
src/goto-instrument/havoc_loops.cpp	0.00% <0.00%> (ø)
src/goto-instrument/loop_utils.cpp	82.85% <66.66%> (ø)
src/goto-instrument/contracts/assigns.h	100.00% <100.00%> (ø)
src/goto-instrument/contracts/contracts.cpp	95.53% <100.00%> (+<0.01%)	⬆️
src/goto-instrument/contracts/utils.h	100.00% <100.00%> (ø)
src/goto-instrument/havoc_utils.cpp	100.00% <100.00%> (ø)
... and 3 more

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