Remove dodgy connection check

[samuong]

This behaviour worked well on some corporate networks, but breaks on others. From now on, users who use a custom PAC file with a file:// URL will need to do this check themselves, before returning a PROXY directive.

Fixes #106

[samhaque]

Hi, could we please get this reviewed and merged, it's blocking a lot of developers who rely on making custom pac files

[samhaque]

Looks like all CI checks passed, could you have a look @camh- @juliaogris @marcelocantos @samuong