Replace unicode characters in comments with ascii

Replace unicode characters in comments with ascii

The unicode characters, while in comments and not code, caused MSVC
to emit compiler warning C4819:

  The file contains a character that cannot be represented in the
  current code page (number).  Save the file in Unicode format to
  prevent data loss.

Fix by replacing the characters in print.c with descriptive comments
containing the codepoints and symbol names, and remove the character
in brin_bloom.c which was a footnote reference copied from the paper
citation.

Per report from hamerkop in the buildfarm.

Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/340E4118-0D0C-4E85-8141-8C40EB22DA3A@yesql.se