vm_call_opt_send should not drop the empty keyword hash

Now the mechanism that conveys kw_splat flag is gradually established,
so the hack to drop the empty keyword hash is not needed for
vm_call_opt_send.

test/ruby/test_keyword.rb

@@ -465,7 +465,9 @@ class TestKeywordArguments < Test::Unit::TestCase
       [arg, args]
     end
     assert_raise(ArgumentError) { c.send(:m, **{}) }
-    assert_raise(ArgumentError) { c.send(:m, **kw) }
+    assert_warn(/The keyword argument is passed as the last hash parameter.* for `m'/m) do
+      assert_equal([kw, kw], c.send(:m, **kw))
+    end
     assert_warn(/The keyword argument is passed as the last hash parameter.* for `m'/m) do
       assert_equal([h, kw], c.send(:m, **h))
     end
@@ -640,7 +642,6 @@ class TestKeywordArguments < Test::Unit::TestCase
       [arg, args]
     end
     assert_raise(ArgumentError) { c.m(**{}) }
-    assert_raise(ArgumentError) { c.send(:m, **kw) } # XXX: fix it after the commit
     assert_warn(/The keyword argument is passed as the last hash parameter.* for `method_missing'/m) do
       assert_equal([kw, kw], c.m(**kw))
     end

vm_insnhelper.c

@@ -2309,7 +2309,7 @@ vm_call_opt_send(rb_execution_context_t *ec, rb_control_frame_t *reg_cfp, struct
     struct rb_call_info_with_kwarg ci_entry;
     struct rb_call_cache cc_entry, *cc;
 
-    CALLER_SETUP_ARG(reg_cfp, calling, orig_ci, 1);
+    CALLER_SETUP_ARG(reg_cfp, calling, orig_ci, 0);
 
     i = calling->argc - 1;