Remove arch package building script that is no longer maintained.

[NlightNFotis]

Last time the file was maintained was 4 years ago. It no longer
makes sense for us to keep it around, as no one maintains it, and
for anyone that wants to use cbmc under Arch Linux, there are
packages in AUR that are better maintained than this one.

• Each commit message has a non-empty body, explaining why the change was made.
• 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).
• My commit message includes data points confirming performance improvements (if claimed).
• My PR is restricted to a single feature or bugfix.
• White-space or formatting changes outside the feature-related changed lines are in commits of their own.

[thomasspriggs]

Makes sense to me. If there is a desire to keep arch package(s) in repository long term, then they would need to be tested in CI.

[NlightNFotis]

In my opinion, we shouldn't be the ones maintaining packages for various distributions.

It's the distributions' responsibility to package CBMC if they want/need it. Otherwise our packages get bit-rotten (like this one that's getting removed) and it increases our load to monitor various distributions for changes and update our build scripts/packages to facilitate them.

In terms of this particular package building script, there's already a more up to date one in AUR https://aur.archlinux.org/packages/cbmc/

[tautschnig]

For traceability, can I ask that the commit message initially be generated using git revert 735c152ce8, and then adding the commit message body that you've got right now? This is a clean revert of 735c152, and we should document that.

[codecov]

Codecov Report

Merging #5854 (aaaf707) into develop (0f9bfa7) will increase coverage by 0.00%.
The diff coverage is 93.69%.

@@           Coverage Diff            @@
##           develop    #5854   +/-   ##
========================================
  Coverage    72.88%   72.88%           
========================================
  Files         1421     1422    +1     
  Lines       154262   154283   +21     
========================================
+ Hits        112434   112455   +21     
  Misses       41828    41828           

Impacted Files	Coverage Δ
src/analyses/goto_check.cpp	88.28% <ø> (ø)
src/util/std_code.h	94.00% <90.90%> (-0.06%)	⬇️
src/util/format_expr.cpp	86.38% <93.02%> (+0.60%)	⬆️
src/goto-instrument/dump_c.cpp	79.97% <100.00%> (-0.08%)	⬇️
src/goto-instrument/goto_program2code.cpp	68.10% <100.00%> (ø)
src/goto-programs/goto_program.h	89.36% <100.00%> (+0.10%)	⬆️
unit/util/format.cpp	100.00% <100.00%> (ø)
src/util/expr_cast.h	94.73% <0.00%> (+0.14%)	⬆️
... and 1 more

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