remove count for google_compute_ssl_certificate

[vchrisb]

Looking at the files I think count for google_compute_ssl_certificate.certificate in module certs can be removed, as the resource is required to be present to create the gorouter LB.

The reason for the ask is, that I want to use an override file to set the var.ssl_cert from a different output (ACME) but can't be done due to the usage of var.ssl_cert to interpolate count via locals. https://github.com/pivotal-cf/terraforming-gcp/blob/43f6eec7bfaea72150dedc4218fcacf94b2cf473/modules/certs/certificate.tf#L2