sysutils/beats7: Remove, and point users to beats8
beats7 uses symbols from Go that were removed in go1.23, making it
unbuildable with anything beyond go1.22. Both go1.22 and go1.23 are EOL,
and I don't know of any way to fix it. It's going to become unsupported
upstream in 13 days, so its time has come.
This commit also includes a MOVED entry that directs users to the
more-modern beats8.