server: remove TLS cert data retrieval over HTTP

Back in CockroachDB v1.1 (v17.2 in the new calver scheme), we
introduced a certificate rotation mechanism. To help
teach/troubleshoot that feature, we also provided a way for the
operator to view the certificate details in the DB Console (expiration
time, addresses, etc.)

This work was done in PR cockroachdb#16087, to solve issues cockroachdb#15027/cockroachdb#1674.

However, as part of that PR, the implementation of the back-end API
also included the *data* of the cert (including the cert signature
and the signature chain) in the response payload.

This additional payload was never used in a user-facing feature: the
DB Console does not display it nor does it contain a link to "download
the cert file". The back-end API is not public either, so we are not
expecting end-users to have legitimate uses for this feature.

Meanwhile, leaking cert data through an API runs dangerously close
to violating PCI guidelines (not quite, since keys are not exposed,
but still...).

So in order to avoid a remark on this during PCI review cycles, and to
remove the chance this will be misused, this patch removes the
data payload from the cert response.

The DB Console screen corresponding to the original work remains
unaffected.

Release note: None

docs/generated/http/full.md

@@ -50,7 +50,6 @@ Support status: [reserved](#support-status)
 | ----- | ---- | ----- | ----------- | -------------- |
 | type | [CertificateDetails.CertificateType](#cockroach.server.serverpb.CertificatesResponse-cockroach.server.serverpb.CertificateDetails.CertificateType) |  |  | [reserved](#support-status) |
 | error_message | [string](#cockroach.server.serverpb.CertificatesResponse-string) |  | "error_message" and "data" are mutually exclusive. | [reserved](#support-status) |
-| data | [bytes](#cockroach.server.serverpb.CertificatesResponse-bytes) |  | data is the raw file contents of the certificate. This means PEM-encoded DER data. | [reserved](#support-status) |
 | fields | [CertificateDetails.Fields](#cockroach.server.serverpb.CertificatesResponse-cockroach.server.serverpb.CertificateDetails.Fields) | repeated |  | [reserved](#support-status) |