While working on, we noticed that we only have to fix the missing UI output to fix the critical part of this issue, so extracting this into a separate issue, will set that back to normal after this.
Expand the field delete form and related base class/trait to support more than one config being deleted, and some changes to make it easier to alter the list as it adds the field that is deleted to the output, which is confusing, so we want to remove that.
Not yet sure about the changes to ManageFieldsTest, might extract that method into a separate test to avoid affecting the existing test.
User interface changes
Data model changes
PASSED: [[SimpleTest]]: [PHP 5.5 MySQL] 114,401 pass(es). View
FAILED: [[SimpleTest]]: [PHP 5.5 MySQL] 114,353 pass(es), 1 fail(s), and 0 exception(s). View
FAILED: [[SimpleTest]]: [PHP 5.5 MySQL] 114,085 pass(es), 4 fail(s), and 1 exception(s). View