This reverts commit ee4d51197f.
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: Ic057a86a67d819e49ff2965bc3387fd63a8e76a4
293786f2a1