CgroupSetupCgroups: don't leak fd.

- If file is unlinked, the mmapped region is still there.
- If file is truncated, a SIGBUS will be seen, and holding
  the fd doesn't help.

Test: boots (sanity)
Bug: 123664216
Change-Id: I6683804bc795fab6798891a4471e5fe58fbffe13
1 file changed