inspector: do not add 'inspector' property

'inspector' property is not an official API and should not be published
on process object, where the user may discover it.

This change was extracted from https://github.com/nodejs/node/pull/12263
that will be focused on creating JS bindings.

PR-URL: https://github.com/nodejs/node/pull/12656


Reviewed-By: Aleksey Kozyatinskiy <kozyatinskiy@chromium.org>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Timothy Gu <timothygu99@gmail.com>