binder_rpc_fuzzer: remove rlimit stuff

Copying from another commit in this project, where I'm doing this:

Originally I was going for a model where too big of allocations are
actually sent to malloc and they fail, but this wasn't really a good
plan:
- allocatoins which are near the maximum can cause arbitrary threads
  to fail even if they allocate just one byte
- Android doesn't use C++ exceptions and the libbinder API freezes
  its use of std::vector. I was looking at forking libstdc++ to fix
  that, but it's overkill
- rlimit doesn't play well with crash_dump* in Android or with the
  fuzzing infrastructure (causes worse stack to get delayed)

Instead, going with this model of only making "reasonable" allocations
to begin with (reject too-big allocations without letting them fail).

Bug: 182938024
Test: binder_rpc_fuzzer for several minutes
Change-Id: I7f34313c5fafe4e54ac05a83be9edd4ed764436f