Issue #2414539 by webflo, vijaycs85: Simplify schema definition for sequence

core/config/schema/core.data_types.schema.yml

core/config/schema/core.entity.schema.yml

core/config/schema/core.extension.schema.yml

core/config/schema/core.menu.schema.yml

core/lib/Drupal/Core/Config/Schema/Sequence.php

core/modules/aggregator/config/schema/aggregator.schema.yml

core/modules/block/config/schema/block.schema.yml

core/modules/book/config/schema/book.schema.yml

core/modules/ckeditor/config/schema/ckeditor.schema.yml

core/modules/color/config/schema/color.schema.yml

core/modules/comment/config/schema/comment.schema.yml

core/modules/config/src/Tests/ConfigSchemaTest.php

...g_schema_test/config/schema/config_schema_test.schema.yml

...ig/tests/config_test/config/schema/config_test.schema.yml

...ion_test/config/schema/config_translation_test.schema.yml

core/modules/contact/config/schema/contact.schema.yml

..._translation/config/schema/content_translation.schema.yml

...ules/contextual/config/schema/contextual.views.schema.yml

...ntity_reference/config/schema/entity_reference.schema.yml

...reference/config/schema/entity_reference.views.schema.yml