Remove custom error component for Duo Enterprise Trial flow

What does this MR do and why?

Fixes: #546199 (closed)

We handled the Duo Pro variation in !189244 (merged) - to use the generic trial failure error. This PR is meant to do the same for the Duo Enterprise variation. Since now are using the default error message and not a custom error message for enterprise or pro, this MR removes the use case of the extra form component.

Was introduced in this discussion, here

Changelog: changed

EE: true

References

Screenshots or screen recordings

Before	After

How to set up and validate locally

Example:

1. Setup GDK to simulate SaaS.
2. Create a new group
3. Make sure the group is on the ultimate plan.
4. In the codebase, make a small change to ensure we trigger the error message.

ee/app/controllers/concerns/gitlab_subscriptions/trials/duo_common.rb

def check_feature_available!
        true
end

def check_trial_eligibility!
        true
end

5. Visit /-/trials/duo_enterprise/new?step=trial
6. Select the group that you created and press Activate my trial
7. This should give the error.

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