Remove DSE metadata, schema parsing, and query-builder extensions

[dkropachev]

Parent: #1025

Why

DSE-specific metadata, schema parsing, and schema-builder syntax are not exercised against ScyllaDB. They expand both the public API and internal schema-maintenance surface.

Scope

• Remove DSE node extras, metadata interfaces/implementations, graph schema metadata, and DSE schema parsers/queries.
• Remove DSE query-builder and schema-builder packages and tests.
• Remove DSE schema integration fixtures and documentation.
• Preserve ordinary Cassandra/Scylla metadata and query-builder behavior.

Acceptance criteria

• No DSE metadata/schema implementation remains.
• No DSE query-builder API remains.
• Ordinary schema and query-builder unit tests pass.
• Relevant metadata integration tests compile and pass.

Dependencies: remove DSE Graph first so graph metadata has no consumers.