chore: eliminate redundant spaces

docs/architecture/system_tables.md

docs/overview/glossary.md

docs/reference/sql/dml.md

docs/reference/sql/dql.md

docs/reference/sql/explain.md

docs/reference/sql/join.md

docs/reference/sql/non_block.md

docs/reference/sql/select.md

docs/tutorial/access_control.md

docs/tutorial/audit_log.md

docs/tutorial/backup.md