tests: Remove support for test directive that is no longer used.
tests: Remove support for test directive that is no longer used.

ae0fdf7a5519a175d887389c80399234637bdc29 changed the setup for the only test
that actually used this.

rust-lang/rust-bindgen,emilio/rust-bindgen,emilio/rust-bindgen,emilio/rust-bindgen,rust-lang/rust-bindgen,emilio/rust-bindgen,emilio/rust-bindgen,rust-lang/rust-bindgen,rust-lang/rust-bindgen