satlab_remote_access: remove unmaintained ctop binary

ctop v0.7.7 is an unmaintained static Go binary from 2022 that is
downloaded from GitHub at build time. It is built with an old Go
toolchain and is responsible for dozens of Go stdlib CVEs reported by
AutoVM against the public satlab_remote_access and satlab-rpcserver
images. Nothing in Satlab references it; use `docker stats` instead.

BUG=b:582199660
TEST=None (build-only change; no other references to ctop)
Change-Id: Id5ecb43da402a16de10fae5712437c1d8e300aa1
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/satlab/+/8798939
Tested-by: Misha Bilyi <mykhailobilyi@google.com>
Reviewed-by: Przemysław Filipek <filipek@google.com>
Reviewed-by: Rafał Gaweł <rafalgawel@google.com>
Commit-Queue: Misha Bilyi <mykhailobilyi@google.com>