Fix macro textual scope shadowing link target

In name resolution, we say that one way in which names introduced by
`use` declarations can be shadowed within a single scope is by macro
textual scope shadowing.  We then linked to a rule that says it's not
an error to define a macro multiple times, but that's discussing only
textual-scope matters.  A `use` declaration creates a path-based scope
binding, so let's point instead to the rule that says that textual
scope name bindings shadow path-based scope bindings.