Remove {f,F}orall_subtypes

[tautschnig]

This was useful in the past, but with C++-11 we can use a ranged-for to
avoid the iterator altogether.

As subtypes are no longer stored in a named sub (removing the
corresponding #if-0-disabled code), the ranged-for can be used directly
without testing for the existence of subtypes beforehand, as the forall
macro did.

• 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 #5783 (22a59fb) into develop (2c11501) will decrease coverage by 0.00%.
The diff coverage is 87.09%.

@@             Coverage Diff             @@
##           develop    #5783      +/-   ##
===========================================
- Coverage    69.67%   69.67%   -0.01%     
===========================================
  Files         1242     1242              
  Lines       100886   100885       -1     
===========================================
- Hits         70291    70290       -1     
  Misses       30595    30595              

Flag	Coverage Δ
cproversmt2	43.37% <44.82%> (-0.01%)	⬇️
regression	66.63% <87.09%> (-0.01%)	⬇️
unit	32.30% <34.48%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/ansi-c/ansi_c_parser.cpp	84.00% <0.00%> (ø)
src/cpp/template_map.cpp	50.00% <0.00%> (ø)
src/util/type.h	100.00% <ø> (ø)
src/ansi-c/ansi_c_convert_type.cpp	82.63% <100.00%> (ø)
src/ansi-c/c_storage_spec.cpp	96.77% <100.00%> (ø)
src/ansi-c/type2name.cpp	95.45% <100.00%> (-0.05%)	⬇️
src/cpp/cpp_declaration.cpp	61.11% <100.00%> (ø)
src/cpp/cpp_storage_spec.cpp	100.00% <100.00%> (ø)
src/cpp/cpp_typecheck_compound_type.cpp	85.69% <100.00%> (ø)
src/goto-instrument/dump_c.cpp	76.89% <100.00%> (ø)
... and 3 more

---

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[hannes-steffenhagen-diffblue]

Seems ok