mbed folder should be removed

All those headers are already deprecated for some time, they should be scheduled to be removed. This issue is a reminder that we should not forget to remove it, most probably the next major version?

Referenced folder: https://github.com/ARMmbed/mbed-drivers/tree/master/mbed

@bremoran @bogdanm

Review the referenced mbed folder at https://github.com/ARMmbed/mbed-drivers/tree/master/mbed and confirm which headers are deprecated. Check the project’s release-version context before removing the folder; done means the deprecated mbed headers are removed in the next major version.

Written by the indexing model from the issue text.