writeback: kill off ->range_cycle option

writeback: kill off ->range_cycle option

All types of writeback are now range cyclic. Kill off the member
from struct wb_writeback_work and struct writeback_control.

Remove the various checks for whether or not this is range cyclic
writeback or not in the writeback code and file systems.

For tracing, we leave the member there, and just always set it to 1.

Signed-off-by: Jens Axboe <axboe@kernel.dk>