Simplify form model updates for new environments form

Description

We currently set a custom shouldBeDestroyed property mark environments for removal, we now use the tokenselector which tracks the list of selected tokens.

Background

The following discussion from !107045 (merged) should be addressed:

• @pgascouvaillancourt started a discussion: (+1 comment)

  question: Was there some reactivity issue when not using Vue.set?

Implementation Guide

• We could probably utilise 2 arrays instead:
  • one for the initialEnvironments in the event of needing to reset
  • another for the current set of selected environments
• We should also address the naming of the add / remove methods