Delay allocating environment locations.

Many environments are killed before we get to the register
allocation, so the early allocation of their locations was
simply wasting memory. For the most expensive method of a
certain app, this reduces EnvLocations with 64-bit dex2oat
from 8657200 to 5339712 (-3.16MiB).

Test: m test-art-host
Test: testrunner.py --host
Bug: 33650849
Change-Id: I70a02fc3c7ec87b54a87e989e1239dc4acfcf18b