Grammar: remove the dead CommandNode.hint_mode field

HintMode became per-node (Node::Hinted) in the node-attached refactor;
the per-command hint_mode field was never the mechanism and is now
read by nothing. Removed the field and its 20 `None` initialisers.

src/dsl/grammar/ddl.rs

@@ -638,36 +638,28 @@ pub static DROP: CommandNode = CommandNode {
         "parse.usage.drop_table",
         "parse.usage.drop_column",
         "parse.usage.drop_relationship",
-    ],
-    hint_mode: None,
-};
+    ],};
 
 pub static ADD: CommandNode = CommandNode {
     entry: Word::keyword("add"),
     shape: ADD_SHAPE,
     ast_builder: build_add,
     help_id: Some("ddl.add"),
-    usage_ids: &["parse.usage.add_column", "parse.usage.add_relationship"],
-    hint_mode: None,
-};
+    usage_ids: &["parse.usage.add_column", "parse.usage.add_relationship"],};
 
 pub static RENAME: CommandNode = CommandNode {
     entry: Word::keyword("rename"),
     shape: RENAME_COLUMN,
     ast_builder: build_rename_column,
     help_id: Some("ddl.rename"),
-    usage_ids: &["parse.usage.rename_column"],
-    hint_mode: None,
-};
+    usage_ids: &["parse.usage.rename_column"],};
 
 pub static CHANGE: CommandNode = CommandNode {
     entry: Word::keyword("change"),
     shape: CHANGE_COLUMN,
     ast_builder: build_change_column,
     help_id: Some("ddl.change"),
-    usage_ids: &["parse.usage.change_column"],
-    hint_mode: None,
-};
+    usage_ids: &["parse.usage.change_column"],};
 
 // =================================================================
 // create_table — `create table <Name> [with pk [<col>:<type>[, ...]]]`
@@ -799,6 +791,4 @@ pub static CREATE: CommandNode = CommandNode {
     shape: CREATE_TABLE,
     ast_builder: build_create_table,
     help_id: Some("ddl.create"),
-    usage_ids: &["parse.usage.create_table"],
-    hint_mode: None,
-};
+    usage_ids: &["parse.usage.create_table"],};