Revert "Issue #2105123 by pwolanin: Add a currentUser() method to \Drupal\Core\Plugin\PluginBase."

Needs more discussion.

This reverts commit feaee01eafc38b43352dbeb8a536db35f2103b26.
Issue #1975490 by ParisLiakos: Convert locale_custom_strings_* to settings.
Issue #1998088 by ParisLiakos, alexpott, ebrowet, plopesc, dawehner, Gábor Hojtsy: Convert locale_translate_english variable to CMI.
Issue #1955378 by skek, Darren Oh, David_Rothstein, claudiu.cristea: Fixed Return same derivative token with path or URI.
Issue #2107309 by amateescu: Fixed Case (in)sensitivity for config entity query.
Issue #2078813 by mr.baileys, ifrik, batigolix, JulienD: Create hook_help() for telephone module.
Issue #1993894 by mgifford, Jelle_S, Wim Leers | jessebeach: Contextual quick edit toggle should be a <a role='button'> not a <a> because it tracks on/off state.
Issue #2108691 by Gábor Hojtsy, linclark, Wim Leers: Two PHPUnit tests not being run.
Issue #2109769 by Wim Leers: CKEditor plugin cache entries should have cache tags.
Issue #1958754 by greyrhino, emma.maria | LewisNyman: Copy improvements to default Views.
Issue #2109553 by lostkangaroo: Add route to resolve update.php path.
Issue #2109601 by tim.plunkett, benjy: Update MAINTAINERS.txt for block.module.
Revert "Issue #2109769 by Wim Leers: CKEditor plugin cache entries should have cache tags."

Needs more discussion.

This reverts commit 477a5673378733d5d2b45ecb10f78ee1a77c499f.
Issue followup #1829224 by ianmthomasuk: Convert the 'theme_default' variable to CMI.
Issue #2109599 by cosmicdreams: Fixed Extra comma in toolbar.js.
Issue #2025451 by amateescu, Berdir | Xano: Fixed Drupal\entity_reference()\Tests\EntityReferenceAdminTest fails on PHP 5.4.9 and libxml 2.9.0.
Issue #2095399 by Berdir: Merge DatabaseStorageController and DatabaseStorageControllerNG.
Issue #2099541 by stefan.r, Schnitzel, Gábor Hojtsy: Fixed ConfigEntities should not load the Entity translated on Edit Forms.
Issue #2099679 by linclark: Fixed Changing the order of asserts in AuthTest::testRead makes them fail.
Issue #2074407 by dawehner, pwolanin: Write tests for hook-based plugin discovery.