[$] Removing read-only transparent huge pages for the page cache

Things do not always go the way kernel developers think they will. Whenthe kernel gained support for the creation of read-only transparent hugepages for the page cache in 2019, the developer of that feature, Song Liu,added aKconfig file entry promising that support for writable hugepages would arrive "in the next few release cycles". Over six yearslater, that promise is still present, but it will never be fulfilled.Instead, the read-only option will soon be removed, reflecting how the coreof the memory-subsystem has changed underneath this particular feature.