internal: remove useless helpers

We generally avoid "syntax only" helper wrappers, which don't do much:
they make code easier to write, but harder to read. They also make
investigations harder, as "find_usages" needs to be invoked both for the
wrapped and unwrapped APIs

crates/rust-analyzer/src/cargo_target_spec.rs

@@ -191,7 +191,7 @@ mod tests {
     use super::*;
 
     use cfg::CfgExpr;
-    use mbe::ast_to_token_tree;
+    use mbe::syntax_node_to_token_tree;
     use syntax::{
         ast::{self, AstNode},
         SmolStr,
@@ -201,7 +201,7 @@ mod tests {
         let cfg_expr = {
             let source_file = ast::SourceFile::parse(cfg).ok().unwrap();
             let tt = source_file.syntax().descendants().find_map(ast::TokenTree::cast).unwrap();
-            let (tt, _) = ast_to_token_tree(&tt);
+            let (tt, _) = syntax_node_to_token_tree(tt.syntax());
             CfgExpr::parse(&tt)
         };