Remove Usage.increment calls that have been shown to in fact be used (#1645)

I think these were added for undocumented features to see if they were
actually used and they were being used.

test/integration/tags/for_tag_test.rb

@@ -450,30 +450,4 @@ HERE
 
     assert(context.registers[:for_stack].empty?)
   end
-
-  def test_instrument_for_offset_continue
-    assert_usage_increment('for_offset_continue') do
-      Template.parse('{% for item in items offset:continue %}{{item}}{% endfor %}')
-    end
-
-    assert_usage_increment('for_offset_continue', times: 0) do
-      Template.parse('{% for item in items offset:2 %}{{item}}{% endfor %}')
-    end
-  end
-
-  def test_instrument_forloop_drop_name
-    assigns = { 'items' => [1, 2, 3, 4, 5] }
-
-    assert_usage_increment('forloop_drop_name', times: 5) do
-      Template.parse('{% for item in items %}{{forloop.name}}{% endfor %}').render!(assigns)
-    end
-
-    assert_usage_increment('forloop_drop_name', times: 0) do
-      Template.parse('{% for item in items %}{{forloop.index}}{% endfor %}').render!(assigns)
-    end
-
-    assert_usage_increment('forloop_drop_name', times: 0) do
-      Template.parse('{% for item in items %}{{item}}{% endfor %}').render!(assigns)
-    end
-  end
 end