Issue #1807556 by Albert Volkman, Lars Toomre: API docs cleanup of Aggregator module

core/modules/aggregator/aggregator.admin.inc

core/modules/aggregator/aggregator.module

core/modules/aggregator/aggregator.pages.inc

core/modules/aggregator/aggregator.processor.inc

core/modules/aggregator/aggregator.theme-rtl.css

core/modules/aggregator/aggregator.theme.css

...regator/lib/Drupal/aggregator/Plugin/FetcherInterface.php

...es/aggregator/lib/Drupal/aggregator/Tests/AddFeedTest.php

...b/Drupal/aggregator/Tests/AggregatorConfigurationTest.php

...egator/lib/Drupal/aggregator/Tests/AggregatorCronTest.php

...r/lib/Drupal/aggregator/Tests/AggregatorRenderingTest.php

...egator/lib/Drupal/aggregator/Tests/AggregatorTestBase.php

...or/lib/Drupal/aggregator/Tests/CategorizeFeedItemTest.php

...egator/lib/Drupal/aggregator/Tests/CategorizeFeedTest.php

...aggregator/lib/Drupal/aggregator/Tests/FeedParserTest.php

...aggregator/lib/Drupal/aggregator/Tests/ImportOpmlTest.php

...egator/lib/Drupal/aggregator/Tests/RemoveFeedItemTest.php

...aggregator/lib/Drupal/aggregator/Tests/RemoveFeedTest.php

...egator/lib/Drupal/aggregator/Tests/UpdateFeedItemTest.php

...aggregator/lib/Drupal/aggregator/Tests/UpdateFeedTest.php