manually fix build_man issue with highlight directive

docs/man/borg-prune.1

@@ -175,20 +175,7 @@ $ borg prune \-v \-\-list \-\-keep\-within=10d \-\-keep\-weekly=4 \-\-keep\-mont
 .UNINDENT
 .UNINDENT
 .sp
-There is also a visualized prune example in \fBdocs/misc/prune\-example.txt\fP:
-.IP "System Message: ERROR/3 (docs/borg-prune.rst:, line 145)"
-Unknown directive type "highlight".
-.INDENT 0.0
-.INDENT 3.5
-.sp
-.nf
-.ft C
-\&.. highlight:: none
-
-.ft P
-.fi
-.UNINDENT
-.UNINDENT
+There is also a visualized prune example in \fBdocs/misc/prune\-example.txt\fP.
 .SH SEE ALSO
 .sp
 \fIborg\-common(1)\fP