Add REMOVE TTL support for ALTER TABLE

Parse ALTER TABLE ... REMOVE TTL command and output the correct
REMOVE_TTL command type in EXPLAIN output.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: kyleconroy

ast/ast.go

@@ -678,6 +678,7 @@ const (
 	AlterDropConstraint    AlterCommandType = "DROP_CONSTRAINT"
 	AlterModifyTTL          AlterCommandType = "MODIFY_TTL"
 	AlterMaterializeTTL     AlterCommandType = "MATERIALIZE_TTL"
+	AlterRemoveTTL          AlterCommandType = "REMOVE_TTL"
 	AlterModifySetting      AlterCommandType = "MODIFY_SETTING"
 	AlterResetSetting       AlterCommandType = "RESET_SETTING"
 	AlterDropPartition         AlterCommandType = "DROP_PARTITION"

parser/parser.go

@@ -5729,6 +5729,10 @@ func (p *Parser) parseAlterCommand() *ast.AlterCommand {
 					p.nextToken() // skip BY
 				}
 				cmd.Type = ast.AlterRemoveSampleBy
+			} else if p.currentIs(token.TTL) {
+				// REMOVE TTL (table-level TTL)
+				p.nextToken() // skip TTL
+				cmd.Type = ast.AlterRemoveTTL
 			}
 		} else if upper == "RESET" {
 			p.nextToken() // skip RESET

parser/testdata/01493_alter_remove_properties/metadata.json

@@ -1,5 +1 @@
-{
-  "explain_todo": {
-    "stmt24": true
-  }
-}
+{}

parser/testdata/01493_alter_remove_properties_zookeeper/metadata.json

@@ -1,5 +1 @@
-{
-  "explain_todo": {
-    "stmt34": true
-  }
-}
+{}