libsyntax: Get rid of obsolete obsolete warning.

src/libsyntax/parse/obsolete.rs

@@ -34,7 +34,6 @@ pub enum ObsoleteSyntax {
     ObsoleteBareFnType,
     ObsoleteNamedExternModule,
     ObsoleteMultipleLocalDecl,
-    ObsoleteMutWithMultipleBindings,
     ObsoleteUnsafeExternFn,
     ObsoleteTraitFuncVisibility,
     ObsoleteConstPointer,
@@ -91,11 +90,6 @@ fn obsolete(&self, sp: Span, kind: ObsoleteSyntax) {
                 "instead of e.g. `let a = 1, b = 2`, write \
                  `let (a, b) = (1, 2)`."
             ),
-            ObsoleteMutWithMultipleBindings => (
-                "`mut` with multiple bindings",
-                "use multiple local declarations instead of e.g. `let mut \
-                 (x, y) = ...`."
-            ),
             ObsoleteUnsafeExternFn => (
                 "unsafe external function",
                 "external functions are always unsafe; remove the `unsafe` \