Remove compiler-builtins from rustc-dep-of-std dependencies

Since [1], this will come automatically from `rustc-std-workspace-core`
and the crates.io dependency should no longer be specified.

Author: tgross35

Cargo.toml

@@ -15,8 +15,7 @@ item that gets emitted.
 edition = "2018"
 
 [dependencies]
-core = { version = "1.0.0", optional = true, package = 'rustc-std-workspace-core' }
-compiler_builtins = { version = '0.1.2', optional = true }
+core = { version = "1.0.0", optional = true, package = "rustc-std-workspace-core" }
 
 [features]
-rustc-dep-of-std = ['core', 'compiler_builtins']
+rustc-dep-of-std = ["core"]