Don't mention cut buffers

We haven't supported them in a long time so we shouldn't mention
them in the interface and documentation.
diff --git a/vncviewer/vncviewer.man b/vncviewer/vncviewer.man
index 4b92b61..9ee616d 100644
--- a/vncviewer/vncviewer.man
+++ b/vncviewer/vncviewer.man
@@ -163,8 +163,8 @@
 .
 .TP
 .B \-SendPrimary
-Send the primary selection and cut buffer to the server as well as the
-clipboard selection. Default is on.
+Send the primary selection to the server as well as the clipboard
+selection. Default is on.
 .
 .TP
 .B \-Maximize