system/lz4: dependency cycle: tests do not depend on python3
Commit 0138941f introduced a dependency cycle involving lz4.
One example of a cycle:
tsort: system/libarchive
tsort: system/libxml2
tsort: system/libxslt
tsort: system/kmod
tsort: system/easy-kernel
tsort: system/python3
tsort: system/lz4
This package does not actually depend on the presence of python3.
Remove it.