The synchronous Scanner is not integrated with ExecPlans and doesn't offer better performance in any case than the asynchronous scanner, so we should start migrating away from the extraneous code path so it can be deprecated and then deleted.

Reporter: Ben Kietzman / @bkietz

Related issues:

• [C++] Remove deprecated Scanner::Scan (relates to)
• [C++][Dataset] Use an ExecPlan for synchronous scans or drop synchronous scans (is related to)

PRs and other links:

• GitHub Pull Request #10749

_{Note: This issue was originally created as ARROW-13338. Please see the migration documentation for further details.}