test: adapt test-v8-flags to V8 9.3

%_IsSmi was removed. %IsSmi can be used instead.

Refs: v8/v8@863a2d6

PR-URL: nodejs#39469
Reviewed-By: Jiawen Geng <technicalcute@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

test/parallel/test-v8-flags.js

@@ -8,11 +8,11 @@ const vm = require('vm');
 // Specifically here, V8 may cache compiled scripts between the flip of the
 // flag. We use a different script each time to work around this problem.
 v8.setFlagsFromString('--allow_natives_syntax');
-assert(eval('%_IsSmi(42)'));
-assert(vm.runInThisContext('%_IsSmi(43)'));
+assert(eval('%IsSmi(42)'));
+assert(vm.runInThisContext('%IsSmi(43)'));
 
 v8.setFlagsFromString('--noallow_natives_syntax');
-assert.throws(function() { eval('%_IsSmi(44)'); },
+assert.throws(function() { eval('%IsSmi(44)'); },
               /^SyntaxError: Unexpected token '%'$/);
-assert.throws(function() { vm.runInThisContext('%_IsSmi(45)'); },
+assert.throws(function() { vm.runInThisContext('%IsSmi(45)'); },
               /^SyntaxError: Unexpected token '%'$/);