This reverts commit 1694f0ce20.
Reason for revert:
It later turned out that setenv does not override os.environ in wsgi
applications and this option can't be used to customize the environment
variable as intended. Let's revert the change to keep the interface
as much simple as possible instead of keeping the useless option.
Change-Id: I9f41273654693c57798c4a34fbc1fe7b535a9ff4
3724ee989c