rustc_span: Remove Symbol::is_doc_keyword.

The check in rustdoc using it is artificial and not helpful.

Author: petrochenkov

compiler/rustc_span/src/symbol.rs

@@ -1556,11 +1556,6 @@ impl Symbol {
         self == kw::Try
     }
 
-    /// Used for sanity checking rustdoc keyword sections.
-    pub fn is_doc_keyword(self) -> bool {
-        self <= kw::Union
-    }
-
     /// A keyword or reserved identifier that can be used as a path segment.
     pub fn is_path_segment_keyword(self) -> bool {
         self == kw::Super

src/librustdoc/clean/mod.rs

@@ -170,11 +170,8 @@ impl Clean<ExternalCrate> for CrateNum {
                 for attr in attrs.lists(sym::doc) {
                     if let Some(v) = attr.value_str() {
                         if attr.has_name(sym::keyword) {
-                            if v.is_doc_keyword() {
-                                keyword = Some(v.to_string());
-                                break;
-                            }
-                            // FIXME: should warn on unknown keywords?
+                            keyword = Some(v.to_string());
+                            break;
                         }
                     }
                 }