printk: Remove console_silent()

It' unused since removal of mn10300:
commit 739d875d ("mn10300: Remove the architecture")
x86 stopped using it in v2.6.12 (see history git):
commit 7574828b ("[PATCH] x86_64: add nmi button support")

Let's clean it up from the header.
Signed-off-by: Dmitry Safonov <dima@arista.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20210727130635.675184-2-dima@arista.com

include/linux/printk.h

@@ -69,11 +69,6 @@ extern int console_printk[];
 #define minimum_console_loglevel (console_printk[2])
 #define default_console_loglevel (console_printk[3])
 
-static inline void console_silent(void)
-{
-	console_loglevel = CONSOLE_LOGLEVEL_SILENT;
-}
-
 static inline void console_verbose(void)
 {
 	if (console_loglevel)