Revert "Set timezone. Fixes #339"

This reverts commit 685798f50a8cd133d4a029fd928de48c1dbf364f.
Jump through hoops to get yesterday's system date. Fixes #339

Changing the Rails timezone (685798f50a8cd133d4a029fd928de48c1dbf364f)
was going too far as this changes ActiveRecord dates and everything.