I changed my mind and also removed the lama benchmarks directories right away
(r3257). They were a subset of the benchmark directories in trunk, minus some
small bugs (like the nonvalidating Assembly tasks from IPC-1998).

Done (last part: r3256). Benchmark directories still exist in the temporal
branches (of course) and in the LAMA branches. We can remove the latter once
we've integrated LAMA.

The benchmarks directories of the various branches should be merged into the trunk.