Remove documentation on change.allowDrafts

This setting applied to the Draft Workflow (draft patch sets), removed
in 2.15 (not to be confused with Draft Comments, which still exist).

Change-Id: Idd5168ffb79c86a381fc721e44f2ff1a0d756df8
diff --git a/Documentation/config-gerrit.txt b/Documentation/config-gerrit.txt
index d241b98..01eca78 100644
--- a/Documentation/config-gerrit.txt
+++ b/Documentation/config-gerrit.txt
@@ -1097,13 +1097,6 @@
 +
 Default is true.
 
-[[change.allowDrafts]]change.allowDrafts::
-+
-Allow drafts workflow. If set to false, drafts cannot be created,
-deleted or published.
-+
-Default is true.
-
 [[change.cacheAutomerge]]change.cacheAutomerge::
 +
 When reviewing diff commits, the left-hand side shows the output of the