[Perl/perl5] f7adb3: perldiag: drop documentation of extinct warning

[Ricardo Signes via perl5-changes]

  Branch: refs/heads/blead
  Home:   https://github.com/Perl/perl5
  Commit: f7adb3411b942711e4c8eedf5a65645bcb405a82
      
https://github.com/Perl/perl5/commit/f7adb3411b942711e4c8eedf5a65645bcb405a82
  Author: Ricardo Signes <rjbs@semiotic.systems>
  Date:   2022-05-26 (Thu, 26 May 2022)

  Changed paths:
    M pod/perldiag.pod

  Log Message:
  -----------
  perldiag: drop documentation of extinct warning

We had a "will be removed in 5.30" warning still documented.  The new
release is 5.36.  This warning is long gone.