Revert "[Fuchsia] TestServer rework for new SSHPortForwarder functionality."

This reverts commit bfb341f2.

Reason for revert: No longer necessary to attempt to expand
SSHPortForwarder's functionality to support bidirectional port mapping.
Original change's description:
> [Fuchsia] TestServer rework for new SSHPortForwarder functionality.
>
> Made a minor change to make sure that SetupTestServer interacts
> properly with the new _ConnectPortForwardingTask and ForwardingScheme
> versions.
>
> Change-Id: I16add737f7595fac416973c1296882f9f40d0dc1
> Reviewed-on: https://chromium-review.googlesource.com/1178381
> Reviewed-by: Kevin Marshall <kmarshall@chromium.org>
> Commit-Queue: Kevin Marshall <kmarshall@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#583900}

TBR=kmarshall@chromium.org,sergeyu@chromium.org,stephanstross@google.com

# Not skipping CQ checks because original CL landed > 1 day ago.

Change-Id: I1fd3a0f48cc21fba0d599a9fba26a62aa04e5dc1
Reviewed-on: https://chromium-review.googlesource.com/1188493
Commit-Queue: Stephan Stross <stephanstross@google.com>
Reviewed-by: Sergey Ulanov <sergeyu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#586081}

build/fuchsia/net_test_server.py

@@ -137,8 +137,8 @@ def SetupTestServer(target, test_concurrency):
   logging.debug('Starting test server.')
   spawning_server = chrome_test_server_spawner.SpawningServer(
       0, SSHPortForwarder(target), test_concurrency)
-  scheme = ForwardingScheme(spawning_server.server_port, 0, True)
-  forwarded_port = _ConnectPortForwardingTask(target, scheme)
+  forwarded_port = _ConnectPortForwardingTask(
+      target, spawning_server.server_port)
   spawning_server.Start()
 
   logging.debug('Test server listening for connections (port=%d)' %