Remove std's dependency on compiler-builtins

`compiler-builtins` is already in the crate graph via `alloc`, and all
features related to `compiler-builtins` goes through `alloc`. There
isn't any reason that `std` needs this direct dependency, so remove it.

Author: tgross35

Cargo.lock

@@ -18,7 +18,6 @@ cfg-if = { version = "1.0", features = ['rustc-dep-of-std'] }
 panic_unwind = { path = "../panic_unwind", optional = true }
 panic_abort = { path = "../panic_abort" }
 core = { path = "../core", public = true }
-compiler_builtins = { path = "../compiler-builtins/compiler-builtins" }
 unwind = { path = "../unwind" }
 hashbrown = { version = "0.15", default-features = false, features = [
     'rustc-dep-of-std',