Remove dfcc_utilst::inhibit_unused_functions

[tautschnig]

This has neither been implemented nor used so far. If a future use is necessary, then this commit should just be reverted.

• 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

Patch coverage has no change and project coverage change: -0.04 ⚠️

Comparison is base (31dfa3e) 78.42% compared to head (5b99a6f) 78.39%.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #7684      +/-   ##
===========================================
- Coverage    78.42%   78.39%   -0.04%     
===========================================
  Files         1674     1674              
  Lines       191948   191946       -2     
===========================================
- Hits        150543   150475      -68     
- Misses       41405    41471      +66     

Impacted Files	Coverage Δ
.../goto-instrument/contracts/dynamic-frames/dfcc.cpp	98.02% <ø> (ø)
...instrument/contracts/dynamic-frames/dfcc_utils.cpp	88.27% <ø> (+0.64%)	⬆️
...o-instrument/contracts/dynamic-frames/dfcc_utils.h	0.00% <ø> (ø)

... and 12 files with indirect coverage changes

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