Maint: OpenVPN option: remove all ping-* options

- Use the built-in healthcheck vpn restart mechanism instead
- Restarting with `ping-restart` or `ping-exit` would only restart with the same `remote` connection
- Specify `ping` options as VPN specific to ensure the server doesn't disconnect us

internal/provider/vpnunlimited/openvpnconf.go

@@ -21,7 +21,6 @@ func (p *Provider) BuildConf(connection models.Connection,
 		// VPNUnlimited specific
 		"reneg-sec 0",
 		"ping 5",
-		"ping-exit 30",
 		"route-metric 1",
 
 		// Added constant values