Delete unused nightly cfg

Author: dtolnay

build.rs

@@ -50,7 +50,6 @@ fn main() {
     if rustc >= 80 {
         println!("cargo:rustc-check-cfg=cfg(doc_cfg)");
         println!("cargo:rustc-check-cfg=cfg(fuzzing)");
-        println!("cargo:rustc-check-cfg=cfg(nightly)");
         println!("cargo:rustc-check-cfg=cfg(no_is_available)");
         println!("cargo:rustc-check-cfg=cfg(no_literal_byte_character)");
         println!("cargo:rustc-check-cfg=cfg(no_literal_c_string)");

tests/test.rs

@@ -541,7 +541,6 @@ testing 123
 }
 
 #[cfg(procmacro2_semver_exempt)]
-#[cfg(not(nightly))]
 #[test]
 fn default_span() {
     let start = Span::call_site().start();