[server] Support DROP COLUMN schema evolution

### Search before asking

- [x] I searched in the [issues](https://github.com/apache/fluss/issues) and found nothing similar.

### Description

Subissue of #1154.

Support `ALTER TABLE ... DROP COLUMN` schema evolution.

- Follow-ups (not in this scope):
- Lake catalog DROP COLUMN (Iceberg / Paimon)
- Spark connector ALTER DDL

### Willingness to contribute

- [x] I'm willing to submit a PR!

Start by tracing the existing server-side schema-evolution handling for ALTER TABLE operations and identify its related tests. Add support for ALTER TABLE ... DROP COLUMN in the server, then verify the behavior with the relevant schema-evolution tests. Keep Lake catalog DROP COLUMN and Spark connector ALTER DDL outside this scope.

Written by the indexing model from the issue text.