fix 400 error for showing problems.

Author: si-yao

Diff for: lib/plugins/leetcode.js

@@ -138,7 +138,6 @@ plugin.getProblem = function(problem, cb) {
       '    enableRunCode',
       '    metaData',
       '    translatedContent',
-      '    discussCategoryId',
       '  }',
       '}'
     ].join('\n'),
@@ -166,7 +165,8 @@ plugin.getProblem = function(problem, cb) {
     problem.testcase = q.sampleTestCase;
     problem.testable = q.enableRunCode;
     problem.templateMeta = JSON.parse(q.metaData);
-    problem.discuss =  q.discussCategoryId;
+    // @si-yao: seems below property is never used.
+    //problem.discuss =  q.discussCategoryId;
 
     return cb(null, problem);
   });