node8: get rid of node < 0.7 compatibility when deleting files.

- path.exists() is no longer part of nodejs
- fs.exists() is deprecated (as of nodejs >= 8)
- checking a file for existence before using it is open to raca condition. It is
  preferable to go ahead and use the file, and eventually handle the error
- we can afford two simple synchronous fs operations here

src/node/handler/ImportHandler.js

@@ -292,16 +292,19 @@ exports.doImport = function(req, res, padId)
         return;
       }
 
-      //for node < 0.7 compatible
+      try {
-      var fileExists = fs.exists || path.exists;
+         fs.unlinkSync(srcFile);
-      async.parallel([
+      } catch (e) {
-        function(callback){
+         console.log(e);
-          fileExists (srcFile, function(exist) { (exist)? fs.unlink(srcFile, callback): callback(); });
+      }
-        },
+
-        function(callback){
+      try {
-          fileExists (destFile, function(exist) { (exist)? fs.unlink(destFile, callback): callback(); });
+         fs.unlinkSync(destFile);
-        }
+      } catch (e) {
-      ], callback);
+         console.log(e);
+      }
+
+      callback();
     }
   ], function(err) {
     var status = "ok";