Remove check keyword identifier check from rustdoc

Author: GuillaumeGomez

Diff for: src/librustdoc/clean/mod.rs

@@ -169,19 +169,7 @@ impl Clean<ExternalCrate> for CrateNum {
                 for attr in attrs.lists(sym::doc) {
                     if attr.has_name(sym::keyword) {
                         if let Some(v) = attr.value_str() {
-                            let k = v.to_string();
-                            if !rustc_lexer::is_ident(&k) {
-                                let sp = get_span(&attr).unwrap_or_else(|| attr.span());
-                                cx.tcx
-                                    .sess
-                                    .struct_span_err(
-                                        sp,
-                                        &format!("`{}` is not a valid identifier", v),
-                                    )
-                                    .emit();
-                            } else {
-                                keyword = Some(k);
-                            }
+                            keyword = Some(v.to_string());
                             break;
                         }
                     }