Fix typo showing error message after destroy page

What does this MR do?

In d8ce327c there was a small refactor to use ServiceResponse in wiki controller actions. Nevertheless, there is a small typo/bug that, when there is an error deleting the page, we show the object string representation instead of the error message.

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Before the MR:

After the MR:

Does this MR meet the acceptance criteria?

Conformity

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