Fix return value of rabbit_priority_queue:delete_crashed/1 (backport #13087)

[mergify]

Proposed Changes

According to the rabbit_backing_queue behavious it must always return ok, but it used to return a list of results one for each priority. That caused the below crash further up the call chain.

> rabbit_classic_queue:delete_crashed(Q)
** exception error: no case clause matching [ok,ok,ok,ok,ok,ok,ok,ok,ok,ok,ok]
     in function  rabbit_classic_queue:delete_crashed/2 (rabbit_classic_queue.erl, line 516)

Other backing_queue implementations (rabbit_variable_queue) just exit with a badmatch upon error.

This (very minor) issue is present since 3.13.0 when rabbit_classic_queue:delete_crashed_in_backing_queue/1 was introduced with Khepri in commit 5f0981c. Before that the result of BQ:delete_crashed/1 was simply ignored.

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This is an automatic backport of pull request #13087 done by [Mergify](https://mergify.com).