remove Canceled from API impl

crates/ra_db/src/cancellation.rs

@@ -21,8 +21,6 @@ pub struct Canceled {
     _private: (),
 }
 
-pub type Cancelable<T> = Result<T, Canceled>;
-
 impl Canceled {
     pub(crate) fn new() -> Canceled {
         Canceled { _private: () }

crates/ra_db/src/lib.rs

@@ -10,7 +10,7 @@ use std::panic;
 use ra_syntax::{TextUnit, TextRange, SourceFile, TreeArc};
 
 pub use crate::{
-    cancellation::{Canceled, Cancelable},
+    cancellation::Canceled,
     syntax_ptr::LocalSyntaxPtr,
     input::{
         FilesDatabase, FileId, CrateId, SourceRoot, SourceRootId, CrateGraph, Dependency,