[docs] updated docs of num_iterations parameter (#1515)

* updated docs of num_iterations parameter

* updated num_iterations param description for R

docs/Parameters.rst

@@ -127,8 +127,6 @@ Core Parameters
 
    -  number of boosting iterations
 
-   -  **Note**: for Python/R-package, **this parameter is ignored**, use ``num_boost_round`` (Python) or ``nrounds`` (R) input arguments of ``train`` and ``cv`` methods instead
-
    -  **Note**: internally, LightGBM constructs ``num_class * num_iterations`` trees for multi-class classification problems
 
 -  ``learning_rate`` :raw-html:`<a id="learning_rate" title="Permalink to this parameter" href="#learning_rate">&#x1F517;&#xFE0E;</a>`, default = ``0.1``, type = double, aliases: ``shrinkage_rate``, ``eta``, constraints: ``learning_rate > 0.0``

include/LightGBM/config.h

@@ -150,7 +150,6 @@ public:
   // alias = num_iteration, n_iter, num_tree, num_trees, num_round, num_rounds, num_boost_round, n_estimators
   // check = >=0
   // desc = number of boosting iterations
-  // desc = **Note**: for Python/R-package, **this parameter is ignored**, use ``num_boost_round`` (Python) or ``nrounds`` (R) input arguments of ``train`` and ``cv`` methods instead
   // desc = **Note**: internally, LightGBM constructs ``num_class * num_iterations`` trees for multi-class classification problems
   int num_iterations = 100;