Remove verbose debug logs from acker (#39672)

Remove some debug log entries about acked events. Those log entries
turn out to be very verbose and of very little use. They do not carry
any information about the acked events, and we already have metrics
about acked events in the 30s metrics and monitoring HTTP endpoint.

(cherry picked from commit 62b4c18)

CHANGELOG-developer.next.asciidoc

@@ -67,6 +67,7 @@ The list below covers the major changes between 7.0.0-rc2 and main only.
 - `queue.ACKListener` has been removed. Queue configurations now accept an explicit callback function for ACK handling. {pull}35078[35078]
 - Split split httpmon out of x-pack/filebeat/input/internal/httplog. {pull}36385[36385]
 - Beats publishing pipeline does not propagate the close signal to its clients any more. It's responsibility of the user to close the pipeline client. {issue}38197[38197] {pull}38556[38556]
+- Debug log entries from the acker (`stateful ack ...` or `stateless ack ...`) removed. {pull}39672[39672]
 
 ==== Bugfixes
 

filebeat/beater/acker.go

@@ -21,7 +21,6 @@ import (
 	"github.com/elastic/beats/v7/filebeat/input/file"
 	"github.com/elastic/beats/v7/libbeat/beat"
 	"github.com/elastic/beats/v7/libbeat/common/acker"
-	"github.com/elastic/elastic-agent-libs/logp"
 )
 
 type statefulLogger interface {
@@ -35,8 +34,6 @@ type statelessLogger interface {
 // eventAcker handles publisher pipeline ACKs and forwards
 // them to the registrar or directly to the stateless logger.
 func eventACKer(statelessOut statelessLogger, statefulOut statefulLogger) beat.EventListener {
-	log := logp.NewLogger("acker")
-
 	return acker.EventPrivateReporter(func(_ int, data []interface{}) {
 		stateless := 0
 		states := make([]file.State, 0, len(data))
@@ -56,12 +53,10 @@ func eventACKer(statelessOut statelessLogger, statefulOut statefulLogger) beat.E
 		}
 
 		if len(states) > 0 {
-			log.Debugw("stateful ack", "count", len(states))
 			statefulOut.Published(states)
 		}
 
 		if stateless > 0 {
-			log.Debugw("stateless ack", "count", stateless)
 			statelessOut.Published(stateless)
 		}
 	})