fix(ui_auth): fix confirmation dialog for unlink account button in profile screen

[Mad-ScientistX]

Description

See https://github.com/firebase/FirebaseUI-Flutter/pull/346 "Previously the wrong navigator was popped when cancelling or confirming the dialog. this resulted in the dialog still beeing visible and the navigator behind it beeing popped. the fix adds the context object to the function parameter, so the right navigator gets popped.".

This same logic needs to be applied to the showUnlinkConfirmationDialog dialog so it obtains the correct context and pops correctly.

Related Issues

fixes https://github.com/firebase/FirebaseUI-Flutter/issues/212

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Breaking Change

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