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.

library/Cargo.lock

@@ -311,7 +311,6 @@ dependencies = [
  "addr2line",
  "alloc",
  "cfg-if",
- "compiler_builtins",
  "core",
  "dlmalloc",
  "fortanix-sgx-abi",

library/std/Cargo.toml

@@ -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',