Removed unneeded code [skip ci]

Author: ankane

test/dmatrix_test.rb

@@ -64,7 +64,6 @@ def test_daru
   def test_numo
     skip if RUBY_PLATFORM == "java"
 
-    require "numo/narray"
     data = Numo::DFloat.new(3, 5).seq
     label = Numo::DFloat.new(3).seq
     XGBoost::DMatrix.new(data, label: label)
@@ -73,7 +72,6 @@ def test_numo
   def test_rover
     skip if RUBY_PLATFORM == "java"
 
-    require "rover"
     data = Rover.read_csv(data_path)
     label = data.delete("y")
     dataset = XGBoost::DMatrix.new(data, label: label)

test/test_helper.rb

@@ -2,10 +2,7 @@
 Bundler.require(:default)
 require "minitest/autorun"
 require "minitest/pride"
-require "csv"
 require "json"
-require "matrix"
-require "daru"
 
 class Minitest::Test
   def assert_elements_in_delta(expected, actual)