Fix confusing example in paste(1)

Paste's man page contains an example for a reimplementation of
nl(1). This example uses the command line
    sed = myfile | paste -s -d '\t\n' - -
in order to concatenate consecutive lines with an intervening tab.

However, the way the example uses the switches -s and -d and two `dash`
input files is redundant. There are in fact two equivalent but simpler
ways to achieve the desired result:
    sed = myfile | paste -s -d '\t\n' -
uses the same style as the previous example, while
    sed = myfile | paste - -
is arguably even simpler and illustrates the final sentence of the
DESCRIPTION.

Reviewed by:		imp@
Pull Request:		https://github.com/freebsd/freebsd-src/pull/163

usr.bin/paste/paste.1

@@ -120,7 +120,7 @@ Combine pairs of lines from a file into single lines:
 Number the lines in a file, similar to
 .Xr nl 1 :
 .Pp
-.Dl "sed = myfile | paste -s -d '\et\en' - -"
+.Dl "sed = myfile | paste - -"
 .Pp
 Create a colon-separated list of directories named
 .Pa bin ,