ci-automation: Remove unnecessary zstd prerequisite check

When running `./run_local_tests.sh`, a warning is printed if `zstd` is
not found in the host environment:

  $ ./run_local_tests.sh arm64 2 cl.cloudinit.script
  ...
  zstd could not be found. unpacking container image may fail.
  ...

This check is performed because `ci-config.env` is sourced by the script.
However, the `run_local_tests.sh` workflow itself does not depend on `zstd`.

The `zstd` command is required for building Flatcar[1], but that
process runs inside the Flatcar SDK container, which is guaranteed to
have `zstd` installed. The check on the host running the local tests is
therefore redundant and produces confusing noise for developers.

This patch removes the check to eliminate the spurious warning.

[1] flatcar/mantle#853 (comment)
Signed-off-by: Li Zhijian <lizhijian@fujitsu.com>

Author: zhijianli88

ci-automation/ci-config.env

@@ -19,11 +19,6 @@ GC_BUCKET="flatcar-linux"
 
 DEFAULT_HTTP_IMAGE_URL_TEMPLATE="@PROTO@://${BUILDCACHE_SERVER}/images/@ARCH@/@VERNUM@"
 
-if ! command -v zstd > /dev/null; then
-  # we require zstd and it is included by default on flatcar
-  echo >&2 "zstd could not be found. unpacking container image may fail."
-fi
-
 CI_GIT_AUTHOR="flatcar-ci"
 CI_GIT_EMAIL="infra+ci@flatcar-linux.org"