doc: fix echo example programs

Adjust to work with self-signed certificates, and certificates that do not name "localhost" as their host name. Removed duplicate examples, they differed only by using pfx. Its not necessary to show every option, and we don't, and the example wouldn't work with most pfx anyway, since it didn't specify a password.

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines