This PR removes the experimental `optimizeImages` flag. This feature was designed to automatically add preload tags for images, but I was never able to get it to do a very good job of selecting the images that actually need preloading.
This feature never graduated from experimental and in fact we never even publicized it as an experimental feature for people to try.
Additionally, even if someone was using this feature, it wouldn't have a functional effect, only a performance effect (removal of some preloads).
For those reasons, I believe it is safe to remove this functionality and that it is not a breaking change.
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