nfscl: Clear out a lot of cruft related to B_DIRECT that is never executed

[rmacklem]

Summary

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.

Test Plan

Tested as a part of the IETF bakeathon this week and no further
crashes occurred. I have also put it through my typical NFS tests.

[kib]

sys/fs/nfsclient/nfs_clbio.c

803

805

1615

Might be assert that B_DIRECT is not set?

sys/fs/nfsclient/nfs_clnfsiod.c

294

Again, assert?

[rmacklem]

Made the changes suggested by kib@.