doc: Remove volume rename from gluster's man page.

Change-Id: I5cde789088417f26d0c8319a1b24fdaa2c37dfe6
BUG:  1031328
Signed-off-by: Vijay Bellur <vbellur@redhat.com>
Reviewed-on: http://review.gluster.org/8656
Reviewed-by: Humble Devassy Chirammal <humble.devassy@gmail.com>
Reviewed-by: Atin Mukherjee <amukherj@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>