Revert "Merge pull request #120 from Jeff-Ciesielski/stm32_cl"

This reverts commit 029bc0ee276cdc0d265a0b3312492159bea5e29e, reversing
changes made to a7b3e99644b69faa87d5cf98a24571f7d060d7ec.

This uses LGPL libopencm3. While the patch doesn't include the code,
the resulting binary would force the release of all code as LGPL.