Clarify enterprise user management removal

What does this MR do and why?

This is a follow on from !138635 (closed) to get the main change committed. Will clarify what happens when an enterprise user is removed from the group separately.

Existing Enterprise documentation has a section entitled 'Dissociation of the user from their enterprise group' which states: Changing an enterprise user’s primary email to an email with a non-verified domain automatically **disassociates** them from their enterprise group.

This is misleading and suggests that an account is removed from the enterprise group once the primary email has been changed. All the email does is remove the enterprise badge and with that the additional management capability that the group owner may have had over the account.

Existing section:

Replaced with:

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