Revert "Skip tests that depend on 8.18.0-SNAPSHOT artifacts being available"

[ycombinator]

Reverts #4133 as it's now possible to create 8.18.0-SNAPSHOT deployments in the ESS production CFT region.

[pierrehilbert]

/test

[ycombinator]

E2E tests are failing like so:

=== RUN   TestAgentInstallSuite
--
  | agent_install_test.go:94:
  | Error Trace:	/opt/buildkite-agent/builds/bk-agent-prod-gcp-1732865060834845856/elastic/fleet-server/testing/e2e/agent_install_test.go:143
  | /opt/buildkite-agent/builds/bk-agent-prod-gcp-1732865060834845856/elastic/fleet-server/testing/e2e/agent_install_test.go:94
  | /opt/buildkite-agent/go/pkg/mod/github.com/stretchr/[email protected]/suite/suite.go:157
  | /opt/buildkite-agent/builds/bk-agent-prod-gcp-1732865060834845856/elastic/fleet-server/testing/e2e/agent_install_test.go:61
  | Error:      	Should be true
  | Test:       	TestAgentInstallSuite
  | Messages:   	unable to find package download for fileName = elastic-agent-8.18.0-SNAPSHOT-linux-x86_64.tar.gz

I'm not really sure why the package is not available for download, given that we have https://snapshots.elastic.co/8.18.0-4aa4b16c/summary-8.18.0-SNAPSHOT.html. @michel-laterman any thoughts?

[michel-laterman]

What the downloadAgent step does is do GET https://artifacts-api.elastic.co/v1/search/$VERSION-SNAPSHOT
then search the returned json body's packages object for the file.

I can see the package name if I manually do the request.

Maybe we should switch the download to GET https://artifacts-api.elastic.co/v1/downloads/elastic-agent-package/elastic-agent-8.18.0-SNAPSHOT-linux-x86_64.tar.gz directly?