Enable Gerrit support in Skia's PostUploadHook

BUG=skia:5676
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2299203002
NOTRY=true

Review-Url: https://codereview.chromium.org/2299203002
diff --git a/PRESUBMIT.py b/PRESUBMIT.py
index f25459e..38b4b5a 100644
--- a/PRESUBMIT.py
+++ b/PRESUBMIT.py
@@ -443,12 +443,6 @@
   """
 
   results = []
-  if cl.IsGerrit():
-    results.append(
-        output_api.PresubmitNotifyResult(
-            'Post upload hooks are not yet supported for Gerrit CLs'))
-    return results
-
   atleast_one_docs_change = False
   all_docs_changes = True
   for affected_file in change.AffectedFiles():