split_cl: do not prepend '/' in $directory

I think it is readable if '/' is not prepended for the CL title like

```
$directory: apply some change
```

e.g. https://crrev.com/c/5541194/1..3//COMMIT_MSG#b7

Change-Id: If4cbb4966ebf62f99a7078028e4cb104de4b7197
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/5540834
Auto-Submit: Takuto Ikuta <tikuta@chromium.org>
Reviewed-by: Gavin Mak <gavinmak@google.com>
Commit-Queue: Gavin Mak <gavinmak@google.com>

split_cl.py

@@ -64,7 +64,7 @@ def FormatDirectoriesForPrinting(directories, prefix=None):
 
 def FormatDescriptionOrComment(txt, directories):
     """Replaces $directory with |directories| in |txt|."""
-    to_insert = FormatDirectoriesForPrinting(directories, prefix='/')
+    to_insert = FormatDirectoriesForPrinting(directories)
     return txt.replace('$directory', to_insert)
 
 

tests/split_cl_test.py

@@ -38,12 +38,14 @@ class SplitClTest(unittest.TestCase):
         # One directory
         self.assertEqual(
             split_cl.FormatDescriptionOrComment(description, ["foo"]),
-            "Converted use of X to Y in /foo.")
+            "Converted use of X to Y in foo.",
+        )
 
         # Many directories
         self.assertEqual(
             split_cl.FormatDescriptionOrComment(description, ["foo", "bar"]),
-            "Converted use of X to Y in ['/foo', '/bar'].")
+            "Converted use of X to Y in ['foo', 'bar'].",
+        )
 
     def GetDirectoryBaseName(self, file_path):
         return os.path.basename(os.path.dirname(file_path))