Remove or use Aggregator's teaser_length setting

I'm biased because I created this issue, but I still think this is a bug. teaser_length is a non-functional admin setting. But it's not worth arguing over. We only need to decide what to do about it.

I'm in favor of eliminating the setting entirely with no further action. As I've become more familiar with this module over the past few months and studied it again tonight, I've come to believe that there isn't any place that we can migrate this setting into. The entity views and Views don't utilize formatters with options. We would have to add something in order to make it do something. It has been non-functional for 8 years. Let's allow it to die quietly. Here's a patch.

+++ b/tests/src/Functional/Update/AggregatorUpdateDeleteTeaserLengthSettingTest.php
@@ -0,0 +1,33 @@
+  /**
+   * Ensure all items in the aggregator_feeds queue are deleted.
+   */
+  public function testUpdateHookN(): void {

I forgot to update this docblock when I copied it from another test I'd written. But I'm not going to bother changing it right now. We'll probably have to update this class's docblock to change the number of the update function it covers anyway. It can be fixed then.

Good to go too after re-roll and fixing comment per #19

Rerolled since the update function number has to be updated.

Rerolled for the 1.x branch.

Automatically closed - issue fixed for 2 weeks with no activity.