Fix issue #144: Update pacfinder_darwin.go to check PAC URL in SCDynamicStoreCopyProxies as fallback

[Enelass]

1) Added Redundant PAC URL Detection Methods in pacfinder_darwin.go

Before:

• Single method for PAC URL detection using SCDynamicStoreCopyValue

After:

• Two methods for PAC URL detection:
  1. Original method using SCDynamicStoreCopyValue
  2. New method using SCDynamicStoreCopyProxies
• Fallback mechanism: if the first method fails, the second is tried

2) pacfinder Test Files deletion: pacfinder_unix_test and pacfinder_darwin_test

Remove GO test files for pacfinder as these fixes weren't of good quality:

• Hardcoded PAC url or http://internal.anz.com/proxy.pac for ANZ an Australian bank.
• And resorting to using bash command scutil --proxy as opposed to the C functions for MacOS System Config

More info here: https://github.com/Enelass/alpaca_pacfinder_darwin_fix/blob/master/Test_Implementation_Issues.md

[Enelass]

Morning @samuong , Are you OK reviewing this PR please ? Let me know if you have any questions.

Regs, Flo

[Enelass]

CLOSING as new PR is sent at https://github.com/samuong/alpaca/pull/154 @samuong