Revert "[exporter][queuebatcher] set feature gate UsePullingBasedExporterQueueBatcher to beta" (#12246)

Reverts #12122

During the revamp of the pull batching work, couple bugs were found:
1.
#12244
2.
#12247

Author: bogdandrutu

.chloggen/set-new-queue-batching-to-beta.yaml

@@ -27,7 +27,7 @@ import (
 
 var usePullingBasedExporterQueueBatcher = featuregate.GlobalRegistry().MustRegister(
 	"exporter.UsePullingBasedExporterQueueBatcher",
-	featuregate.StageBeta,
+	featuregate.StageAlpha,
 	featuregate.WithRegisterFromVersion("v0.115.0"),
 	featuregate.WithRegisterDescription("if set to true, turns on the pulling-based exporter queue bathcer"),
 )

exporter/exporterhelper/internal/base_exporter.go

@@ -374,14 +374,6 @@ func TestBatchSender_ConcurrencyLimitReached(t *testing.T) {
 			expectedItems:    51,
 		},
 	}
-
-	// Why do we not expect the same behavior when usePullingBasedExporterQueueBatcher is true?
-	// This test checks that when concurrency limit of batch_sender is reached, the batch_sender will flush immediately.
-	// To avoid blocking, the concurrency limit is set to the number of concurrent goroutines that are in charge of
-	// reading from the queue and adding to batch. With the new model, we are pulling instead of pushing so we don't
-	// block the reading goroutine anymore.
-	defer setFeatureGateForTest(t, usePullingBasedExporterQueueBatcher, false)()
-
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
 			qCfg := exporterqueue.NewDefaultConfig()