Check that device file exists first before reverting.

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

Index: scripts/slave/recipe_modules/chromium_android/example.expected/no_cache_builder_basic.json
diff --git a/scripts/slave/recipe_modules/chromium_android/example.expected/no_cache_builder_basic.json b/scripts/slave/recipe_modules/chromium_android/example.expected/no_cache_builder_basic.json
index 6576d99d5bf84def0d23508f3957bc31f9f22e80..b57051a78cfb1e686d20b2ee83818f201de552af 100644
--- a/scripts/slave/recipe_modules/chromium_android/example.expected/no_cache_builder_basic.json
+++ b/scripts/slave/recipe_modules/chromium_android/example.expected/no_cache_builder_basic.json
@@ -269,24 +269,6 @@
     "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",
@@ -419,24 +401,6 @@
     "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",