jobs: remove unnecessary test for batch jobs creation

Commit cockroachdb#67991 introduced a test that turned out to be flaky.
The test runs out of memory sometimes as it creates a very
large batch of jobs. Nevertheless, the test doesn't contribute
much value to the test suite because it only creates a large
batch of jobs. The core functionality is already being tested
with moderately large batch sizes. Therefore, the test is now
removed in this commit.

Release note: None

Fixes: cockroachdb#68962

pkg/jobs/registry_test.go

@@ -299,7 +299,6 @@ func TestBatchJobsCreation(t *testing.T) {
 		{"small batch", 10},
 		{"medium batch", 501},
 		{"large batch", 1001},
-		{"extra large batch", 5001},
 	} {
 		t.Run(test.name, func(t *testing.T) {
 			{