Check that device file exists first before reverting.

scripts/slave/recipe_modules/chromium_android/example.expected/basic_builder_basic.json

Index: scripts/slave/recipe_modules/chromium_android/example.expected/basic_builder_basic.json
diff --git a/scripts/slave/recipe_modules/chromium_android/example.expected/basic_builder_basic.json b/scripts/slave/recipe_modules/chromium_android/example.expected/basic_builder_basic.json
index 5dba7c57f8b77d792b3e700e47f35b433b73102a..4d4bc571dea258c1ae9d6b2f87f8c8bbd2bc4385 100644
--- a/scripts/slave/recipe_modules/chromium_android/example.expected/basic_builder_basic.json
+++ b/scripts/slave/recipe_modules/chromium_android/example.expected/basic_builder_basic.json
@@ -288,24 +288,6 @@
     "name": "authorize_adb_devices"
   },
   {
-    "cmd": [],
-    "name": "fix_device_file_format"
-  },
-  {
-    "cmd": [
-      "python",
-      "-u",
-      "\nimport shutil\nimport sys\nshutil.copy(sys.argv[1], sys.argv[2])\n",
-      "[BUILD]/site_config/.known_devices",
-      "/path/to/tmp/"
-    ],
-    "name": "fix_device_file_format.read_device_file",
-    "~followup_annotations": [
-      "@@@STEP_NEST_LEVEL@1@@@",
-      "@@@STEP_TEXT@file format is compatible@@@"
-    ]
-  },
-  {
     "cmd": [
       "[SLAVE_BUILD]/src/build/android/buildbot/bb_device_status_check.py",
       "--adb-path",
@@ -438,24 +420,6 @@
     "name": "provision_devices"
   },
   {
-    "cmd": [],
-    "name": "fix_device_file_format (2)"
-  },
-  {
-    "cmd": [
-      "python",
-      "-u",
-      "\nimport shutil\nimport sys\nshutil.copy(sys.argv[1], sys.argv[2])\n",
-      "[BUILD]/site_config/.known_devices",
-      "/path/to/tmp/"
-    ],
-    "name": "fix_device_file_format.read_device_file (2)",
-    "~followup_annotations": [
-      "@@@STEP_NEST_LEVEL@1@@@",
-      "@@@STEP_TEXT@file format is compatible@@@"
-    ]
-  },
-  {
     "cmd": [
       "[SLAVE_BUILD]/src/build/android/buildbot/bb_device_status_check.py",
       "--adb-path",