nginx: Remove SSL client certificate support config

[brontolosone]

Following up on this discussion comment, we may want to cut down on useless config noise by removing ssl_trusted_certificate directives from the nginx config.

[alxndrsn]

I think the docs at https://nginx.org/en/docs/http/ngx_http_ssl_module.html#ssl_trusted_certificate, ssl_trusted_certificate are saying that ssl_trusted_certificate is is only relevant when either:

1. ssl_verify_client is enabled, or
2. ssl_stapling is enabled

Neither of these is used in this repo.

[matthew-white]

Closed by #2033.