Remove PLATFORMIO define from test build.
Simplify note-c subtree and add a script for updating it. (#122) Prior to this commit, we were including everything from note-c. Now, we've removed all the unneeded subdirectories, most notably test/, which caused all sorts of problems because the Arduino build system has no way of ignoring folders. In the future, when note-c needs to be bumped, use scripts/upate_note_c.sh.