Update to 5.500
    
    - New upstream release 5.500:
      - cleanup: IO-Stringy is no longer used
      - cleanup: remove auto_install from Makefile.PL
      - RT#22684: fix deadlock in filter() when invoking external programs
        such as gzip
      - RT#60931: if preamble is empty, make sure it's still empty after
        round-tripping through MIME::Entity
      - RT#63739: properly decode RFC2231 encodings in attachment filenames
    - New build requirements:
      - perl(IO::Handle)
      - perl(Mail::Field) >= 1.05
      - perl(Mail::Header) >= 1.01
      - perl(Mail::Internet) >= 1.0203
      - perl(Test::Deep)
    - Drop buildreq perl(IO::Stringy)