Rename MockDatabase -> TestDB

Actually working rename is sooo useful!

crates/ra_hir/src/lib.rs

@@ -29,8 +29,6 @@ macro_rules! impl_froms {
 pub mod debug;
 
 pub mod db;
-#[macro_use]
-pub mod mock;
 pub mod source_binder;
 
 mod ids;
@@ -51,6 +49,8 @@ mod code_model;
 
 pub mod from_source;
 
+#[cfg(test)]
+mod test_db;
 #[cfg(test)]
 mod marks;