chore(tests): drop orphan diagnostic scripts not part of bats suite

- tests/performance_uninstall_scan.sh: standalone perf benchmark with no
  caller, superseded by tests/core_performance.bats and the timing
  assertions in tests/uninstall_scan_bash32.bats.
- tests/test_diagnostic_reports_standalone.sh: one-off diagnostic for
  issue #441; not run by scripts/test.sh.

Updated a comment in uninstall_scan_bash32.bats that pointed to the
deleted perf script.