Related to https://github.com/searxng/searxng/issues/1326
URL for the logo is referenced twice:
* in index.html for preloading: it contains the hash for cache busting (when static_use_hash: true)
* in searxng.min.css: to actually display the image. The URL doesn't contain the hash.
So the image preload actually loads twice the same image.
This commit removed the image preloading.
This is workaround: the real fix is to be able to use the URL with the hash in the CSS.