Remove `mosys platform model` from FW updater

This replicates the functionality intended by chromium:1934715.
The original CL had to be reverted because ToT Autotest was trying to
rely on fallback commands introduced to cros_config in a branch.
(Revert CL: chromium:1937664)
This new CL addresses the original problem by using fallback commands
built into autotest.

BUG=chromium:1023647
TEST=firmware_FAFTRPC.updater on both a unibuild and non-unibuild board

Change-Id: I40adcf6f29465da1cd8bb3265ad5ac94dc3f8de1
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/autotest/+/1984612
Tested-by: Greg Edelston <gredelston@google.com>
Commit-Queue: Greg Edelston <gredelston@google.com>
Reviewed-by: Dana Goyette <dgoyette@chromium.org>
diff --git a/client/cros/faft/utils/firmware_updater.py b/client/cros/faft/utils/firmware_updater.py
index 6efabed..6a06efd 100644
--- a/client/cros/faft/utils/firmware_updater.py
+++ b/client/cros/faft/utils/firmware_updater.py
@@ -11,6 +11,7 @@
 
 from autotest_lib.client.common_lib import error
 from autotest_lib.client.common_lib.cros import chip_utils
+from autotest_lib.client.common_lib.cros import cros_config
 from autotest_lib.client.cros.faft.utils import flashrom_handler
 
 
@@ -403,8 +404,8 @@
                           If None (default), read from extracted manifest.json.
         @type shellball: str | None
         """
-        model_result = self.os_if.run_shell_command_get_output(
-                'mosys platform model')
+        model_result = cros_config.call_cros_config_get_output(
+                '/ name', self.os_if.run_shell_command)
 
         if not model_result:
             return