satlab-rpcserver: Fix base image REGISTRY_URI and Cloud Build dependency

Remove the duplicate ARG REGISTRY_URI=gcr.io/chromeos-partner-moblab
line in src/dockerfiles/satlab-rpcserver/Dockerfile so that
satlab-rpcserver defaults to pulling satlab_remote_access from
us-docker.pkg.dev/chromeos-partner-moblab/satlab rather than the stale
legacy gcr.io image (which contained gevent 21.1.2, CVE-2023-41419).

Also add satlab-remote-access to waitFor for satlab-rpcserver in
src/cloudbuild.yaml so satlab-rpcserver builds against the freshly built
satlab_remote_access image.

BUG=b:571264295
TEST=manual

Change-Id: I103702dad49b448abdcd7fc99885799e9039e851
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/satlab/+/8642069
Reviewed-by: Rafał Gaweł <rafalgawel@google.com>
Tested-by: Tomasz Jakubowski <jakubowskit@google.com>
Commit-Queue: Tomasz Jakubowski <jakubowskit@google.com>