doc/texi2pod.pl: drop unnecessary rule, which was converting "\," to ","

I cannot find a reason for such a rule, which was resulting in badly
escaped filtergraph snippets.

Fix trac ticket #1610.

doc/texi2pod.pl

@@ -211,7 +211,6 @@ INF: while(<$inf>) {
     s/\@TeX\{\}/TeX/g;
     s/\@pounds\{\}/\#/g;
     s/\@minus(?:\{\})?/-/g;
-    s/\\,/,/g;
 
     # Now the ones that have to be replaced by special escapes
     # (which will be turned back into text by unmunge())