um: Remove obsolete reenable_XX calls

reenable_fd has been a NOP since the introduction of the EPOLL
based interrupt controller.
reenable_channel() is no longer needed as the flow control is
now handled via the write IRQs on the channel.

Signed-off-by: Anton Ivanov <anton.ivanov@cambridgegreys.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

arch/um/include/shared/irq_user.h

@@ -31,7 +31,6 @@ struct irq_fd {
 struct siginfo;
 extern void sigio_handler(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs);
 extern void free_irq_by_fd(int fd);
-extern void reactivate_fd(int fd, int irqnum);
 extern void deactivate_fd(int fd, int irqnum);
 extern int deactivate_all_fds(void);
 extern int activate_ipi(int fd, int pid);