remove find_use_placement

A more robust solution to finding where to place use suggestions was added.
The algorithm uses the AST to find the span for the suggestion so we pass this span
down to the HIR during lowering and use it.

Signed-off-by: Miguel Guarniz <mi9uel9@gmail.com>

compiler/rustc_save_analysis/src/lib.rs

@@ -282,7 +282,7 @@ impl<'tcx> SaveContext<'tcx> {
                 let qualname = format!("::{}", self.tcx.def_path_str(def_id));
 
                 let sm = self.tcx.sess.source_map();
-                let filename = sm.span_to_filename(m.inner);
+                let filename = sm.span_to_filename(m.spans.inner_span);
 
                 filter!(self.span_utils, item.ident.span);