Remove duplicate no-built-in-assertions help output

[tautschnig]

With 415c1a3 and 93bd022 merged around the same time, this duplication
likely resulted from a mistake in resolving conflicts. Just remove one
of the lines.

• 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 #5992 (72d84b8) into develop (e76d811) will decrease coverage by 1.10%.
The diff coverage is 85.18%.

@@             Coverage Diff             @@
##           develop    #5992      +/-   ##
===========================================
- Coverage    75.12%   74.02%   -1.11%     
===========================================
  Files         1435     1444       +9     
  Lines       156301   157307    +1006     
===========================================
- Hits        117416   116441     -975     
- Misses       38885    40866    +1981     

Impacted Files	Coverage Δ
src/solvers/smt2/smt2_conv.h	100.00% <ø> (ø)
src/memory-analyzer/gdb_api.cpp	86.89% <50.00%> (ø)
unit/memory-analyzer/gdb_api.cpp	86.46% <94.73%> (ø)
src/solvers/smt2/smt2_conv.cpp	59.95% <100.00%> (+0.56%)	⬆️
src/goto-programs/link_goto_model.cpp	0.00% <0.00%> (-77.97%)	⬇️
...rc/ansi-c/c_typecheck_gcc_polymorphic_builtins.cpp	51.96% <0.00%> (-24.62%)	⬇️
src/goto-programs/remove_returns.cpp	74.84% <0.00%> (-24.53%)	⬇️
src/ansi-c/c_typecheck_base.cpp	55.37% <0.00%> (-22.87%)	⬇️
src/ansi-c/scanner.l	41.15% <0.00%> (-20.58%)	⬇️
src/ansi-c/literals/convert_float_literal.cpp	73.80% <0.00%> (-19.05%)	⬇️
... and 53 more

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[martin-cs]

Happy to merge but I don't understand why the codecov task is failing.