src: remove _third_party_main support

Since 7dead8440c, there is a more official alternative that is
tested and comes with a proper API, and since a6c57cc66d, the
`LoadEnvironment(env)` overload is deprecated, which is the closest
thing we can achieve to deprecating `_third_party_main` support.

Thus, we can now consider us able to remove `_third_party_main`
support.

Fixes: https://github.com/nodejs/node/issues/24017
Refs: https://github.com/nodejs/node/pull/30467
Refs: https://github.com/nodejs/node/pull/32858

PR-URL: https://github.com/nodejs/node/pull/33971
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>

lib/internal/cli_table.js

@@ -11,8 +11,7 @@ const { getStringWidth } = require('internal/util/inspect');
 // The use of Unicode characters below is the only non-comment use of non-ASCII
 // Unicode characters in Node.js built-in modules. If they are ever removed or
 // rewritten with \u escapes, then a test will need to be (re-)added to Node.js
-// core to verify that Unicode characters work in built-ins. Otherwise,
-// consumers using Unicode in _third_party_main.js will run into problems.
+// core to verify that Unicode characters work in built-ins.
 // Refs: https://github.com/nodejs/node/issues/10673
 const tableChars = {
   /* eslint-disable node-core/non-ascii-character */