AIX: make osi_procname a stub

AIX: make osi_procname a stub

'curproc', 'curthread', or other such conveniences do not exist on
AIX, so the current osi_procname implementation breaks the build.

Determining the current process name on AIX is, while possible,
difficult and error-prone. Since we only need the process name for
informational messages to users, don't bother trying to determine it,
and just return the empty string so we can build.

Change-Id: I452a9786d809c3dee3da519cd3d6ca053f8d7ab8
Reviewed-on: http://gerrit.openafs.org/2094
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>