Drop one once_cell dep

Author: matklad

Cargo.lock

@@ -19,8 +19,6 @@ join_to_string = "0.1.3"
 log = "0.4.8"
 rustc-hash = "1.1.0"
 rand = { version = "0.7.3", features = ["small_rng"] }
-# TODO: check if can remove
-once_cell = "1.3.1"
 
 ra_syntax = { path = "../ra_syntax" }
 ra_text_edit = { path = "../ra_text_edit" }