[Perl/perl5] c4c0f5: regcomp.c - remove (**{ ... }) from the regex engine

[Yves Orton via perl5-changes]

  Branch: refs/heads/yves/remove_optimstic_postponed_eval
  Home:   https://github.com/Perl/perl5
  Commit: c4c0f563bdcda931d985859a15e29b60eac1ba05
      
https://github.com/Perl/perl5/commit/c4c0f563bdcda931d985859a15e29b60eac1ba05
  Author: Yves Orton <demer...@gmail.com>
  Date:   2023-02-07 (Tue, 07 Feb 2023)

  Changed paths:
    M pod/perl5378delta.pod
    M pod/perldelta.pod
    M pod/perlre.pod
    M regcomp.c
    M regexec.c
    M t/re/pat_re_eval.t
    M toke.c

  Log Message:
  -----------
  regcomp.c - remove (**{ ... }) from the regex engine

Dave M pointed out that this idea was flawed, and after some
testing I have come to agree with him. This removes it. It was
only available for 5.37.8, so no deprecation cycle involved.