osd, osdc: drop the unused outdata feature of PGLSFilter.

osd, osdc: drop the unused outdata feature of PGLSFilter.

Before this commit PGLSFilter interface was offering the outdata
parameter in its filter() method:

  filter(..., bufferlist& outdata)

OSD was serializing and appending the bufferlist to response to
CEPH_OSD_OP_PGLS_FILTER and CEPH_OSD_OP_PGNLS_FILTER operations.
At the Objecter's side these extra bits were being parsed and
finally stored in NListContext::extra_info. However, it really
looks this member is not used anywhere.

The commit removes the outdata handling on multiple layers: from
PGLSFilter implementations, through OSD till Objecter.

Signed-off-by: Radoslaw Zarzynski <rzarzyns@redhat.com>