The original author agreed to the BSD license by pushing mireq/minetest-mapper-cpp@07067f443d to his own repository.
Thus the addition of a BSD license in commit 7e3e0a067c3a85f69d63f0849a1c621d45419ad9 was not a mistake and is valid.
This commit removes the LGPL license and unnecessary FreeBSD mention in COPYING (which isn't part of BSD 2-Clause anyway).