Remove old kernel from the repository

Currently, this repository retains numerous older kernel versions. Their patch files significantly inflate the repository's overall size (currently 1.7GB). Perhaps we could remove some end-of-life (EOL) stable releases? Alternatively, should we only retain the final minor version of each major release? --- 目前此仓库中保留了很多老版本内核，它们的补丁文件导致整个仓库的体积变大（目前仓库整体体积已有 1.7GB） 也许可以移除一些 EOL 的稳定版？ 或者只保留每个大版本的最后一个小版本？