Revert "Merge pull request #750 from stan-dev/fix-stanc3-dev-mode-mkdir"
Revert "Merge pull request #750 from stan-dev/fix-stanc3-dev-mode-mkdir"

This reverts commit 29186eebcefd496f3ca7c139e372064ac28b445d, reversing
changes made to 6f6e6be4367a2514e67f83337ace8b058ad20b94.

stan-dev/cmdstan,stan-dev/cmdstan,stan-dev/cmdstan,stan-dev/cmdstan