Remove invalid array syntax from cipher-suites.mdx

[nisbet-hubbard]

Summary

nginx’s ssl_ciphers directive only accepts comma or space-separated strings: https://docs.openssl.org/master/man1/openssl-ciphers/#cipher-list-format

The array syntax was from CF’s API.

Screenshots (optional)

Documentation checklist

• The documentation style guide has been adhered to.

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