assert-single-alias in ns/rebuild.clj is dead code

[bbatsov]

refactor-nrepl.ns.rebuild/assert-single-alias builds a for expression that throws on mismatched aliases, then discards the result and returns alias. Because for is lazy, the assertion never fires.

The kondo bump in #(this-PR) flagged it. The straightforward fix (doseq instead of for) makes the assertion fire and breaks 29 tests that rely on calling this with alias = nil or "". Need to figure out the intended contract — either make those callers pass a real alias, or change assert-single-alias to be a no-op explicitly (and drop the body).

For now there's a #_:clj-kondo/ignore to keep CI green.