8080471: fix usage of replace and file separator in Nashorn tests
Summary: Two tests should use replace instead of replaceAll, and there is a typo in the usage of File.separator.
Reviewed-by: attila, hannesw
with_stat.js:2:1 "with" statement cannot be used in strict mode
with({}) {}
^
with_stat.js:2:7 Expected ; but found )
with({}) {}
^
repeat_param.js:2:15 strict mode function cannot have duplicate parameter name "x"
function func(x, x) {}
^
repeat_prop.js:2:22 Property "foo" already defined
var obj = { foo: 34, foo: 'hello' };
^