recipe engine: remove explicit cwd default in step recipe module

recipe_modules/path/example.expected/linux_swarming.json

Index: recipe_modules/path/example.expected/linux_swarming.json
diff --git a/recipe_modules/path/example.expected/linux_swarming.json b/recipe_modules/path/example.expected/linux_swarming.json
index fdfa97805a71e4edc36e64beecde60f8676a32e0..88be1162fe4f0ac8178e1aa717263bd27e4009d8 100644
--- a/recipe_modules/path/example.expected/linux_swarming.json
+++ b/recipe_modules/path/example.expected/linux_swarming.json
@@ -4,7 +4,6 @@
       "/bin/echo",
       "[SLAVE_BUILD]/foo"
     ],
-    "cwd": "[SLAVE_BUILD]",
     "name": "step1"
   },
   {
@@ -12,7 +11,6 @@
       "echo",
       "RECIPE_MODULE[recipe_engine::path]/resources/dir/file.py"
     ],
-    "cwd": "[SLAVE_BUILD]",
     "name": "print resource"
   },
   {
@@ -20,7 +18,6 @@
       "echo",
       "RECIPE_PACKAGE_REPO[recipe_engine]/dir/file.py"
     ],
-    "cwd": "[SLAVE_BUILD]",
     "name": "print package dir"
   },
   {
@@ -28,7 +25,6 @@
       "/bin/echo",
       "[SLAVE_BUILD]/checkout/jerky"
     ],
-    "cwd": "[SLAVE_BUILD]",
     "name": "checkout path"
   },
   {
@@ -36,7 +32,6 @@
       "touch",
       "[SLAVE_BUILD]/new_file"
     ],
-    "cwd": "[SLAVE_BUILD]",
     "name": "touch me"
   },
   {