Drop KFunction.isTailrec

The fate of this modifier seems unclear, and there doesn't seem to be any
valuable use cases for it in reflection

core/runtime.jvm/src/kotlin/jvm/internal/FunctionReference.java

@@ -61,11 +61,6 @@ public class FunctionReference extends CallableReference implements FunctionImpl
         return getReflected().isInfix();
     }
 
-    @Override
-    public boolean isTailrec() {
-        return getReflected().isTailrec();
-    }
-
     @Override
     public boolean isSuspend() {
         return getReflected().isSuspend();