Remove obsolete rules to build runtests

Runtests are built by testrunner.py, remove the rule that builds
them as part of checkbuild.  This removes the only rule that
causes Jack to run when ANDROID_COMPILE_WITH_JACK=false.

Test: m -j ANDROID_COMPILE_WITH_JACK=false tests checkbuild
Change-Id: Ib0aa48836fbca9056e9dca3500b0d4dae29977aa