## What changes were proposed in this pull request?
Coincidentally, I discovered that a couple images were unused in `docs/`, and then searched and found more, and then realized some PNGs were pretty big and could be crushed, and before I knew it, had done the same for the ASF site (not committed yet).
No functional change at all, just less superfluous image data.
## How was this patch tested?
`jekyll serve`
Author: Sean Owen <sowen@cloudera.com>
Closes#14029 from srowen/RemoveCompressImages.
## What changes were proposed in this pull request?
Use new Spark logo including "Apache" (now, with crushed PNGs). Remove old unreferenced logo files.
## How was this patch tested?
Manual check of generated HTML site and Spark UI. I searched for references to the deleted files to make sure they were not used.
Author: Sean Owen <sowen@cloudera.com>
Closes#13609 from srowen/SPARK-15879.
