lib,test: remove lib/internal/test/unicode.js

Remove lib/internal/test/unicode.js and associated test. When we added
the file and test, only comments in lib had non-ASCII characters. Now,
lib/internal/cli_table.js has non-ASCII characters. Tests that exercise
the `console.table()` therefore fulfill the need to test non-ASCII
characters in built-in modules.

PR-URL: https://github.com/nodejs/node/pull/25298


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>