nfscl: Clear out a lot of cruft related to B_DIRECT

There is only one place in the unpatched sources where B_DIRECT is
set in the NFS client and this code is never executed. As such, this patch
removes this code that is never executed, since B_DIRECT should never
be set.

During a IETF testing event this week, I saw a crash in ncl_doio_directwrite(),
but this function is only called if B_DIRECT is set.
I cannot explain how ncl_doio_directwrite() got called, but once this patch
was applied to the sources, the crash did not recur. This is not surprising,
since this patch deleted the function.

(cherry picked from commit 03a39a17089adc1d0e28076670e664dcdebccf73)