adb: temporarily kill adb_benchmark.

Temporarily delete adb_benchmark, since it seems difficult to make this
sensibly work with a single target that's used for both libadb and
libadbd benchmarking.

Bug: http://b/150317254
Test: treehugger
Change-Id: Ibf81fdff4f2b7304b586ce9a7955b4bc2c11484e