I agree with you and the commenters who have expressed concern regarding this question's deletion. The number one rule when moderating Stack Overflow—whether as a regular community member or as a diamond moderator—should be not to destroy value. In other words, don't make the Internet a worse place by removing useful information.
In this case, it is pretty clear that the information is useful, based solely on the vote counts. The question is scored at +26/−0, while the top answer is scored at +63/−0. None of the 13,000 viewers found either of these to be unclear, not useful, or otherwise not helpful. That's a pretty strong signal, and overriding it must be done with extreme care.
Yvette has already copped to having made a mistake here. She handled a "not an answer" flag on the self-answer, and after reading that answer, concluded that the question was due to an issue that could not be reproduced and thus this Q&A would not be helpful to others in the future. There's a close reason specifically for that (under list of "off-topic" reasons), and it's a perfectly valid reason to close and/or remove questions.
When moderators are cleaning up low-quality answers, it's important that they also take the time to see if the question itself might be responsible for attracting those low-quality answers. If so, the question itself should be cleaned up, not just the answers. In other words: focus on the cause, not the symptoms.
This turned out to be a bit of an edge case, though. Despite the unhelpful self-answer, this problem does seem to be something that strikes a large number of people, and was resolved in a way that is massively helpful to future viewers. As such, the deletion was a simple mistake, and has since been corrected. Thanks for bringing it to our attention; please put away your pitchforks now. :-)
In the future, it's worth noting that mistakes like this can also be brought to the moderator team's attention by raising a custom flag on the deleted question (possible as long as you have privileges to see deleted posts) or on another question. I don't mean this suggestion as a way of discouraging posting on Meta when you actually want community input, but sometimes the Meta effect is undesirable.
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