Issue #2372507 by dawehner, mavimo, RavindraSingh: Remove _system_path from $request->attributes

core/core.services.yml

core/includes/theme.inc

...l/Core/EventSubscriber/DefaultExceptionHtmlSubscriber.php

...rupal/Core/EventSubscriber/ExceptionLoggingSubscriber.php

core/lib/Drupal/Core/EventSubscriber/PathSubscriber.php

core/lib/Drupal/Core/Form/FormSubmitter.php

core/lib/Drupal/Core/Path/CurrentPathStack.php

.../lib/Drupal/Core/RouteProcessor/RouteProcessorCurrent.php

core/lib/Drupal/Core/Routing/RouteProvider.php

core/lib/Drupal/Core/Routing/UrlMatcher.php

core/modules/system/src/PathBasedBreadcrumbBuilder.php

core/modules/system/src/Plugin/Condition/RequestPath.php

...modules/system/src/Tests/Form/ElementsTableSelectTest.php

...les/system/src/Tests/Plugin/Condition/RequestPathTest.php

...s/RouteProcessor/RouteProcessorCurrentIntegrationTest.php

core/modules/system/src/Tests/Routing/RouteProviderTest.php

core/modules/system/system.services.yml

...es/theme_test/src/EventSubscriber/ThemeTestSubscriber.php

...s/system/tests/modules/theme_test/theme_test.services.yml

...s/src/Unit/Breadcrumbs/PathBasedBreadcrumbBuilderTest.php