Simplify ToHashByHashCode

(cherry picked from commit 9ed5948)

Author: eregon

src/main/java/org/truffleruby/core/hash/HashingNodes.java

@@ -11,6 +11,7 @@
 
 import com.oracle.truffle.api.dsl.Cached;
 import com.oracle.truffle.api.dsl.CachedContext;
+import com.oracle.truffle.api.dsl.Fallback;
 import com.oracle.truffle.api.dsl.GenerateUncached;
 import com.oracle.truffle.api.dsl.Specialization;
 import org.truffleruby.RubyContext;
@@ -25,7 +26,6 @@
 import org.truffleruby.core.symbol.SymbolNodes;
 import org.truffleruby.core.string.ImmutableRubyString;
 import org.truffleruby.language.RubyBaseNode;
-import org.truffleruby.language.RubyGuards;
 import org.truffleruby.language.dispatch.DispatchNode;
 
 public abstract class HashingNodes {
@@ -109,24 +109,18 @@ protected int hashImmutableString(ImmutableRubyString value,
             return (int) stringHashNode.execute(value);
         }
 
-
         @Specialization
         protected int hashSymbol(RubySymbol value,
                 @Cached SymbolNodes.HashSymbolNode symbolHashNode) {
             return (int) symbolHashNode.execute(value);
         }
 
-        @Specialization(guards = "!isSpecialized(value)")
+        @Fallback
         protected int hash(Object value,
                 @Cached DispatchNode callHash,
                 @Cached HashCastResultNode cast) {
             return cast.execute(callHash.call(value, "hash"));
         }
-
-        protected static boolean isSpecialized(Object value) {
-            return RubyGuards.isPrimitive(value) || value instanceof RubyBignum || value instanceof RubyString ||
-                    value instanceof ImmutableRubyString || value instanceof RubySymbol;
-        }
     }
 
     @GenerateUncached