lib: removed unnecessary fs.realpath `options` arg check + tests

Removed duplicated check for options argument of fs.realpath.

Added some tests which covering the cases for passing options arg
as null.

PR-URL: https://github.com/nodejs/node/pull/27909


Reviewed-By: Ujjwal Sharma <usharma1998@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>