build-unit-test-docker: remove span-lite

There are no uses of span-lite within the openbmc org anymore and
everyone should be using `std::span` now.  Remove it from the Docker
container.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I09ceea13678c364ecd331c243aa4476bd0cf2ee4
1 file changed