remove packager-cli.js and so, remove dependency on spawn-rx

[develar]

As electron-forge and electron-builder are able to to pack electron-compile projects, no need anymore in the packager-cli.js

Removing packager-cli.js will also allow us to remove spawn-rx dependency. To avoid unnecessary dependencies in the production app.

Side note: electron-builder automatically detects that spawn-rx must be unpacked (due to Jobber.exe) and creates app.asar.unpacked directory. It is yet another reason why I want to remove this dependency.

If you don't mind, I can prepare PR.