SSH Upload using proxy regardless of preference settings on Win 10 (1.8.3)

If a system proxy is set on Windows 10, the SSH upload will fail. This happens even when I have set the Arduino proxy settings to "no proxy" in the network tab.

Upload works as expected if the system proxy is turned off.

The proxy server shows no connections, so I'm not sure what is happening there, but tcpdump on the proxy, and wireshark on the desktop both show connections from the desktop to the proxy on the proxy port.

Here is the Arduino error - it basically says it cannot establish a socket, which leads me to believe that it is, for some reason, trying to SSH into the proxy server on the proxy port:

```
Sketch uses 3800 bytes (11%) of program storage space. Maximum is 32256 bytes.
Global variables use 314 bytes (15%) of dynamic memory, leaving 1734 bytes for local variables. Maximum is 2048 bytes.
processing.app.debug.RunnerException
at cc.arduino.packages.uploaders.SSHUploader.uploadUsingPreferences(SSHUploader.java:145)
at cc.arduino.UploaderUtils.upload(UploaderUtils.java:78)
at processing.app.SketchController.upload(SketchController.java:713)
at processing.app.SketchController.exportApplet(SketchController.java:686)
at processing.app.Editor$DefaultExportHandler.run(Editor.java:2149)
at java.lang.Thread.run(Thread.java:745)
Caused by: com.jcraft.jsch.JSchException: timeout: socket is not established
at com.jcraft.jsch.Util.createSocket(Util.java:389)
at com.jcraft.jsch.Session.connect(Session.java:215)
at cc.arduino.packages.uploaders.SSHUploader.uploadUsingPreferences(SSHUploader.java:117)
... 5 more
```

Start in SSHUploader.java, especially uploadUsingPreferences at the stack-trace lines, and trace how the proxy preference reaches the JSch session; UploaderUtils.java is the upload entry point. Reproduce with a Windows system proxy and Arduino's "no proxy" setting, then verify SSH upload no longer connects through the proxy when that preference is selected.

Written by the indexing model from the issue text.