tests: bluetooth: Remove broken ECC unit tests

These are currently failing CI and don't really have a maintainer or
someone who'd fully understand how they're supposed to work. Let's remove
them for now and longer term work on reintroducing them in a form that's
maintainable and understood by people actively developing the Bluetooth
host stack.

Signed-off-by: Johan Hedberg <johan.hedberg@silabs.com>

Author: jhedberg