AMA installer wrongly assumes if config file exists then ARC is installed even though it isn't

[irusensei]

Agent assumes that if ArcSettingsFile exists then ARC is installed. Problem is that removing the ARC RPM doesn't remove ArcSettingsFile.

This caused a bit of confusion on some VMs where a while ago ARC was accidentally installed on Azure VMs but was later removed. AMA picked old proxy configurations from that file that prevented AMA from sending logs.

https://github.com/Azure/azure-linux-extensions/blob/master/AzureMonitorAgent/agent.py#L797-L800

Thanks.