Remove visitTimechart

Signed-off-by: Yuanchun Shen <yuanchu@amazon.com>

Author: yuancu

core/src/main/java/org/opensearch/sql/ast/tree/Timechart.java

@@ -34,6 +34,7 @@
 import org.opensearch.sql.ast.AbstractNodeVisitor;
 import org.opensearch.sql.ast.dsl.AstDSL;
 import org.opensearch.sql.ast.expression.AggregateFunction;
+import org.opensearch.sql.ast.expression.Argument;
 import org.opensearch.sql.ast.expression.Field;
 import org.opensearch.sql.ast.expression.Function;
 import org.opensearch.sql.ast.expression.IntervalUnit;