EnvironmentIndicatorDeleteForm is unused

Problem/Motivation

EnvironmentIndicatorDeleteForm is not declared anywhere, and the entity type is actually using the default form:

> * "delete" = "Drupal\Core\Entity\EntityDeleteForm"

It looks like EnvironmentIndicatorDeleteForm needs some work anyway, and should also be changed to use EntityDeleteForm as a parent.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes