Revert "Refactor pre-installation check to use promise pattern"

This reverts commit 7e0dcef0166afb0e6a834efda7b1e1435fd866bd.
Revert "Use "which npm package" instead of literally executing UNIX "which" command"

This reverts commit 031f98db04e68fb06daf985f35264edd026c4b28.
Revert "Abort installation if PhantomJS is already installed"

This reverts commit 053c931981a3b5180532d2771acc8a48d648dc56.