Remove special casing for library symbols

We might as well handle them internally, via queries.

I am not sure, but it looks like the current LibraryData setup might
even predate salsa? It's not really needed and creates a bunch of
complexity.

crates/ra_ide/src/lib.rs

@@ -82,7 +82,7 @@ pub use ra_db::{
     Canceled, CrateGraph, CrateId, Edition, FileId, FilePosition, FileRange, SourceRootId,
 };
 pub use ra_ide_db::{
-    change::{AnalysisChange, LibraryData},
+    change::AnalysisChange,
     line_index::{LineCol, LineIndex},
     search::SearchScope,
     source_change::{FileSystemEdit, SourceChange, SourceFileEdit},