Revert "Migrate libcore benchmarks to BenchmarkRule"

This reverts commit e292bf87.

Reason for revert: This has been causing failures and is not does not seem compatible with the CB dashboard
(cherry picked from https://android-review.googlesource.com/q/commit:13e69db0dbbf5e354fd80082e07814caf88cd9b7)
Merged-In: Iea68da6aae4d5cc4f72b65268e522e22e34b45fe
Change-Id: Iea68da6aae4d5cc4f72b65268e522e22e34b45fe