Remove heartbeat from bundled beats in agent.

This keeps most of the changes in
elastic#20488 but unbundles heartbeat
since it's not ready for prime time yet. We may as well keep the work
that has been done already IMHO.

x-pack/elastic-agent/CHANGELOG.next.asciidoc

@@ -21,7 +21,6 @@
 - Improved version CLI {pull}20359[20359]
 - Enroll CLI now restarts running daemon {pull}20359[20359]
 - Add restart CLI cmd {pull}20359[20359]
-- Add new `synthetics/*` inputs to run Heartbeat {pull}20387[20387]
 - Users of the Docker image can now pass `FLEET_ENROLL_INSECURE=1` to include the `--insecure` flag with the `elastic-agent enroll` command {issue}20312[20312] {pull}20713[20713]
 - Add `docker` composable dynamic provider. {pull}20842[20842]
 - Add support for dynamic inputs with providers and `{{variable|"default"}}` substitution. {pull}20839[20839]

x-pack/elastic-agent/magefile.go

@@ -572,7 +572,7 @@ func packageAgent(requiredPackages []string, packagingFn func()) {
 		defer os.RemoveAll(dropPath)
 		defer os.Unsetenv(agentDropPath)
 
-		packedBeats := []string{"filebeat", "heartbeat", "metricbeat"}
+		packedBeats := []string{"filebeat", "metricbeat"}
 
 		for _, b := range packedBeats {
 			pwd, err := filepath.Abs(filepath.Join("..", b))