remote: turn GetAgent() into a property

This makes the API a bit cleaner.

BUG=b:187791211
TEST=CQ passes

Change-Id: I83f790c269c7578c5ae96cecec6f53fe1404993a
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/3860483
Reviewed-by: Sergey Frolov <sfrolov@google.com>
Tested-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
diff --git a/scripts/cros_gdb.py b/scripts/cros_gdb.py
index 9ea800b..d21ebb1 100644
--- a/scripts/cros_gdb.py
+++ b/scripts/cros_gdb.py
@@ -487,7 +487,7 @@
             ]
 
         if device:
-            ssh_cmd = device.GetAgent().GetSSHCommand(self.ssh_settings)
+            ssh_cmd = device.agent.GetSSHCommand(self.ssh_settings)
 
             ssh_cmd.extend(["--", "gdbserver"])