test: remove third argument from assert.strictEqual()

`test/parallel/test-util-inspect.js` has a call to
`assert.strictEqual()` that receives three arguments.
The third argument is a string literal. Unfortunately,
calling assert.strictEqual() this way means that if
there is an AssertionError, the value of the variables
pos and npos are not reported.
This PR removes this argument.

PR-URL: https://github.com/nodejs/node/pull/22371


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Jon Moss <me@jonathanmoss.me>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: George Adams <george.adams@uk.ibm.com>