docbook: move pipe and splice to filesystems docbook

Move pipes and splice docbook to filesystems book.
kernel-api book is huge (10x most other books) & slow to process.

Signed-off-by: Randy Dunlap <[email protected]>
Cc: Jens Axboe <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
2 files changed