xen/pv_console: Fix MISRA C 2012 Rule 2.1 violation

Remove the definition of the function pv_console_evtchn(),
when CONFIG_XEN_GUEST is not set, because the function is not used.

Signed-off-by: Xenia Ragiadakou <burzalodowa@gmail.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Tested-by: Jiamei Xie <jiamei.xie@arm.com> # arm64

xen/include/xen/pv_console.h

@@ -19,11 +19,6 @@ static inline void pv_console_set_rx_handler(serial_rx_fn fn) { }
 static inline void pv_console_init_postirq(void) { }
 static inline void pv_console_puts(const char *buf, size_t nr) { }
 static inline size_t pv_console_rx(struct cpu_user_regs *regs) { return 0; }
-evtchn_port_t pv_console_evtchn(void)
-{
-    ASSERT_UNREACHABLE();
-    return 0;
-}
 
 #endif /* !CONFIG_XEN_GUEST */
 #endif /* __XEN_PV_CONSOLE_H__ */