vos: Remove pthread send/receive select()

vos: Remove pthread send/receive select()

Commit 65e701fee4968b17066bb81e25b7adaa4024d4f3 introduced a couple of
select() calls when the pthreaded vos writes to or reads from a usd
pipe, corresponding to the IOMGR_Select() calls in LWP. However, these
select() calls are unnecessary, since the read() or write() calls
themselves will block anyway. The reason they are there for LWP is so
the IOMGR can run another process while we're waiting for the file
descriptor to be ready.

The select() in ReceiveFile currently incorrectly waits for the output
to be ready for reading, even though we're trying to write to it. As a
result, if we try to 'vos dump' to a pipe with the pthreaded vos (such
as stdout), we will hang forever, since it will never be ready for
reading.

To fix this, just get rid of the select() calls, since they don't
really do anything.

FIXES 131749

Change-Id: Ibe8841e0c01f1e55ac4ca1a8a99ab71083654662
Reviewed-on: http://gerrit.openafs.org/10360
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Tested-by: BuildBot <buildbot@rampaginggeek.com>