Add deprecation warning for intrinsic __CPROVER_allocated_memory

[NlightNFotis]

In line with #6872, this PR adds a deprecation warning for the usage of the intrinsic __CPROVER_allocated_memory.

Fixes: #6872

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[tautschnig]

You might just use one of the existing tests that currently use __CPROVER_allocated_memory to add a pattern.

[codecov]

Codecov Report

Merging #6876 (ece1a84) into develop (f7a33df) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff            @@
##           develop    #6876   +/-   ##
========================================
  Coverage    77.81%   77.81%           
========================================
  Files         1568     1568           
  Lines       179985   179994    +9     
========================================
+ Hits        140054   140063    +9     
  Misses       39931    39931           

Impacted Files	Coverage Δ
src/ansi-c/goto_check_c.cpp	91.55% <100.00%> (+0.07%)	⬆️

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[NlightNFotis]

@tautschnig Yeah, that's what I was planning to do :)

[TGWDB]

Happy to approve as is, but note that if we're starting to plan Version 6 changes and deprecations, we may want a macro or standard way to implement deprecation warnings.

[NlightNFotis]

@kroening Hi Daniel, this is blocked on a code owner's review from you. Could you please have a look when you find some time? Thank you 👍🏻