Revert "sched: sched_fair.c tweaks"

This reverts commit 03eba852fe44be74e2832e3aa24716aff4e54f1e.
Revert "lib/checksum.c: optimize do_csum a bit"

This reverts commit a506d37c7944be6352be5574fdd00b59dafa5c0d.
Revert "ARM: rwlocks: remove unused branch labels from trylock routines"

This reverts commit 5873dd978cb1850b8ae7dda9d5d49a0d48d326be.