Revert "lots of work on altitude control, UNTESTED"

This reverts commit 00f80fb907816c0848a73623b2992b4bc48d4b41.
Revert "re-add altitude hold, this isn't tested, but will only be active if enabled from the RC"

This reverts commit 7fdb75e066b343deceeb1af1b908b9b1dafb5d2a.