Remove validate var

Not sure why this is here. Maybe it used to need to be mutated in an old
incarnation of this code.

src/fallback.rs

@@ -673,12 +673,11 @@ pub(crate) fn is_ident_continue(c: char) -> bool {
 }
 
 fn validate_ident(string: &str, raw: bool) {
-    let validate = string;
-    if validate.is_empty() {
+    if string.is_empty() {
         panic!("Ident is not allowed to be empty; use Option<Ident>");
     }
 
-    if validate.bytes().all(|digit| digit >= b'0' && digit <= b'9') {
+    if string.bytes().all(|digit| digit >= b'0' && digit <= b'9') {
         panic!("Ident cannot be a number; use Literal instead");
     }
 
@@ -696,7 +695,7 @@ fn validate_ident(string: &str, raw: bool) {
         true
     }
 
-    if !ident_ok(validate) {
+    if !ident_ok(string) {
         panic!("{:?} is not a valid Ident", string);
     }