Drop ciphersuites blacklisted by HTTP/2 spec

Teleport 4.0+ partially switched to GRPC and HTTP/2 as an API protocol. As a result of this, the following ciphers are no longer supported:

    # remove those two ciphersuites from the 
    ciphersuites:
       - tls-rsa-with-aes-128-gcm-sha256
       - tls-rsa-with-aes-256-gcm-sha384

Those two ciphers are banned by HTTP2 RFC spec:

https://tools.ietf.org/html/rfc7540#appendix-A

Whenever Teleport is using those cipher suites, it may experience connectivity issues between components starting 4.0+