external/caliper: remove usages of deprecated org.mockito.runners

The MockitoJUnitRunner was moved to org.mockito.junit, and
the deprecated version in the old package has been removed
upstream. Remove remaining usages to unblock the upgrade.

Test: m checkbuild
Flag: TEST_ONLY
Bug: 310268946
Change-Id: I162f7cceacb21ddda8408ee53a257eaf511c6b4a