[YottaDB/DB/YDB#780] [V70000] Replace --utf8 default usages with --utf8

[YottaDB/DB/YDB#780 (closed)] [V70000] Remove out-of-date OctoVistA.md file

• The objective of this commit started out to replace --utf8 default usages in OctoVistA.md with --utf8.

  Per http://tinco.pair.com/bhaskar/gtm/doc/articles/GTM_V7.0-000_Release_Notes.html#GTM-8263,

  The gtminstall script wrapper (gtminstall.sh) picks up the default ICU version of the system; previously it accepted ICU version specification with a --utf8 option.

  As part of merging GT.M V7.0-000, this was adopted into YDB/sr_unix/ydbinstall.sh. That meant all usages of ydbinstall.sh no longer need to supply --utf8 default. It is enough to just say --utf8.

  Note that ydbinstall.sh still supports the --utf8 default sytnax for backward compatibility but it is not recommended which is why this commit replaces all such references in the YDBOctoVistA repo.

• But @shabiel pointed out that OctoVistA.md is out-of-date and not needed in the repository at all. So this commit just deletes that file.