cl-structures: Remove arena.rs and hashbrown dependency

compiler/cl-structures/Cargo.toml

@@ -8,5 +8,4 @@ license.workspace = true
 publish.workspace = true
 
 [dependencies]
-hashbrown = { version = "0.14.3", default-features = false }
 cl-arena = { path = "../cl-arena" }

compiler/cl-structures/src/arena.rs

@@ -1,7 +0,0 @@
-//! Simple arena-like allocation
-
-pub mod global_intern;
-pub mod intern;
-pub mod string_arena;
-pub mod symbol;
-

compiler/cl-structures/src/lib.rs

@@ -5,8 +5,6 @@
 #![feature(inline_const, dropck_eyepatch, decl_macro, get_many_mut)]
 #![deny(unsafe_op_in_unsafe_fn)]
 
-pub mod arena;
-
 pub mod intern;
 
 pub mod span;