Move is_ascii_ident to where it's used.

compiler/rustc_session/src/utils.rs

@@ -158,14 +158,3 @@ pub fn extra_compiler_flags() -> Option<(Vec<String>, bool)> {
 
     if !result.is_empty() { Some((result, excluded_cargo_defaults)) } else { None }
 }
-
-pub(crate) fn is_ascii_ident(string: &str) -> bool {
-    let mut chars = string.chars();
-    if let Some(start) = chars.next()
-        && (start.is_ascii_alphabetic() || start == '_')
-    {
-        chars.all(|char| char.is_ascii_alphanumeric() || char == '_')
-    } else {
-        false
-    }
-}