Proj cannot run when cloned inside of FlexFlow repository

[elliottslaughter]

If you clone FlexFlow and then clone proj inside of it, tools like dtgen will discover proj's own dtg files and thus fail to execute. E.g.:

git clone https://github.com/flexflow/flexflow-train.git
cd flexflow-train
git clone https://github.com/lockshaw/proj.git
# install proj and attempt to use `proj dtgen`