There are three sets of files in the kernel source tree that, best I can tell, are not used and haven't been touched in years.
There are still some working files from the K1 migration for 2.5 in the ./allkernelpoms file and ./conversion directory. A patch to remove these is attached as "remove-K1-conversion-working-files.patch".
There are multiple incomplete copies of the script and config files for the 2.5 content conversion process in ./tools, ./content-tools, and ./alternative-tools. A patch to remove these is attached as "remove-content-conversion-scripts.patch".
There are various files related to an autobuilt project site that contain no useful content and have not been touched since the kernel project was created in ./src/site, ./kernel-site, ./kernel-util/src/site, and ./kernel-storage-util/src/site. Additionally, there's a module reference to kernel-site in ./pom.xml. A patch to remove these is attached as "remove-website-remnants.patch".