stdio: Get rid of dead code, i.e. stdio_deregister()

Nobody is using stdio_deregister(), remove for good.

Note, even its parameters are not consistent with stdio_register().
So, if anyone want to introduce this again, better with some consistency.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
diff --git a/common/stdio.c b/common/stdio.c
index 2b883fd..acc65ad 100644
--- a/common/stdio.c
+++ b/common/stdio.c
@@ -261,17 +261,6 @@
 	return 0;
 }
 
-int stdio_deregister(const char *devname, int force)
-{
-	struct stdio_dev *dev;
-
-	dev = stdio_get_by_name(devname);
-	if (!dev) /* device not found */
-		return -ENODEV;
-
-	return stdio_deregister_dev(dev, force);
-}
-
 int stdio_init_tables(void)
 {
 #if defined(CONFIG_NEEDS_MANUAL_RELOC)
diff --git a/include/stdio_dev.h b/include/stdio_dev.h
index 48871a6..109a68d 100644
--- a/include/stdio_dev.h
+++ b/include/stdio_dev.h
@@ -83,7 +83,6 @@
 int stdio_init(void);
 
 void stdio_print_current_devices(void);
-int stdio_deregister(const char *devname, int force);
 
 /**
  * stdio_deregister_dev() - deregister the device "devname".