tests/core/search-plugins: Update for performance
tests/core/search-plugins: Update for performance

Part of #156. Though the performance benefit is only about 0.2s on my
MacBook Pro, this eliminates a `while` loop and removes several
vestigial `test_printf` calls, which should reflect a marked improvement
in performance on Windows. However, this is an improvement to the
existing code regardless.

mbland/go-script-bash