html: use xsltproc from PATH

* src/print-xml.c (print_html):
* src/reader.c (prepare_percent_define_front_end_variables):
Drop undocumented support for lines like ‘%define tool.xsltproc
"whatever"’, as this can cause more trouble than it cures.

src/print-xml.c

@@ -543,10 +543,9 @@ print_html (void)
   assert (xml_flag);
 
   char *xml2html = xpath_join (pkgdatadir (), "xslt/xml2xhtml.xsl");
-  char *xsltproc = muscle_percent_define_get ("tool.xsltproc");
   char const *argv[11];
   int i = 0;
-  argv[i++] = xsltproc;
+  argv[i++] = "xsltproc";
   argv[i++] = "-o";
   argv[i++] = spec_html_file;
   argv[i++] = xml2html;
@@ -573,6 +572,5 @@ print_html (void)
                /* termsigp */ NULL);
   if (status)
     complain (NULL, complaint, _("%s failed with status %d"), argv[0], status);
-  free (xsltproc);
   free (xml2html);
 }

src/reader.c

@@ -788,7 +788,6 @@ prepare_percent_define_front_end_variables (void)
       muscle_percent_define_default ("lr.default-reduction", "accepting");
     free (lr_type);
   }
-  muscle_percent_define_default ("tool.xsltproc", "xsltproc");
 
   /* Check %define front-end variables.  */
   {