faft: Simplify Alex/ZGB flow which needs a transition state to enter dev mode

Treats this special case in a new FAFT config: need_dev_transition.

BUG=chrome-os-partner:16231
TEST=None, new devices don't use this logic.

Change-Id: Iff9dbe644f09dd3fe5bf6c2e05d2a2c513db3e82
Reviewed-on: https://chromium-review.googlesource.com/271281
Trybot-Ready: Tom Tam <waihong@google.com>
Tested-by: Tom Tam <waihong@google.com>
Reviewed-by: Yusuf Mohsinally <mohsinally@chromium.org>
Commit-Queue: Tom Tam <waihong@google.com>
diff --git a/server/cros/faft/firmware_test.py b/server/cros/faft/firmware_test.py
index 365021ab..31c98d3 100644
--- a/server/cros/faft/firmware_test.py
+++ b/server/cros/faft/firmware_test.py
@@ -702,12 +702,8 @@
         time.sleep(self.faft_config.firmware_screen)
         self.servo.ctrl_u()
 
-    def wait_fw_screen_and_trigger_recovery(self, need_dev_transition=False):
-        """Wait for firmware warning screen and trigger recovery boot.
-
-        @param need_dev_transition: True when needs dev mode transition, only
-                                    for Alex/ZGB.
-        """
+    def wait_fw_screen_and_trigger_recovery(self):
+        """Wait for firmware warning screen and trigger recovery boot."""
         time.sleep(self.faft_config.firmware_screen)
 
         # Pressing Enter for too long triggers a second key press.
@@ -716,7 +712,7 @@
 
         # For Alex/ZGB, there is a dev warning screen in text mode.
         # Skip it by pressing Ctrl-D.
-        if need_dev_transition:
+        if self.faft_config.need_dev_transition:
             time.sleep(self.faft_config.legacy_text_screen)
             self.servo.ctrl_d()