indexer: Don't overwrite man page contents when hash already exist

Performance improvement. The ON CONFLICT DO UPDATE was primarily to make
sure that old man pages would get fixed when the indexer did a better
job at detecting the encoding, but there haven't been any relevant fixes
to the indexer lately so this forced-update won't do much now.

indexer/src/pkg.rs

@@ -119,12 +119,8 @@ fn insert_man(tr: &postgres::GenericConnection, verid: i32, paths: &[&str], ent:
         cont = cont.replace(0 as char, "");
     }
 
-    // Overwrite entry if the contents are different. It's possible that earlier decoding
-    // implementations didn't properly detect the encoding. (On the other hand, due to differences
-    // in filenames it's also possible that THIS decoding step went wrong, but that's slightly less
-    // likely)
     tr.execute(
-        "INSERT INTO contents (hash, content) VALUES($1, $2) ON CONFLICT (hash) DO UPDATE SET content = $2",
+        "INSERT INTO contents (hash, content) VALUES($1, $2) ON CONFLICT (hash) DO NOTHING",
         &[&dig.as_ref(), &cont]
     ).unwrap();