Make e2e signed_in_as_user more efficient

What does this MR do and why?

Removes an unnecessary wait from signed_in_as_user?.

Saves 10 seconds on tests that use signed_in_as_user? when already logged out.

Example spec: qa/specs/features/browser_ui/10_govern/user/impersonation_token_spec.rb

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.