Remove duplicate __weak_reference definition

__weak_reference is defined both in cdefs.h and sys/cdefs.h this causes
build errors if both files are included. Remove __weak_reference definition
from cdefs.h

Signed-off-by: Imre Kis <imre.kis@arm.com>
Change-Id: If9e31c1d3216f8433166cafc9c2fdd959a45c0ba
diff --git a/components/common/libc/include/cdefs.h b/components/common/libc/include/cdefs.h
index b11d072..75e9bbb 100644
--- a/components/common/libc/include/cdefs.h
+++ b/components/common/libc/include/cdefs.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018-2022, Arm Limited and Contributors. All rights reserved.
+ * Copyright (c) 2018-2024, Arm Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -29,10 +29,6 @@
 #define __printflike(fmtarg, firstvararg) \
 		__attribute__((__format__ (__printf__, fmtarg, firstvararg)))
 
-#define __weak_reference(sym, alias)	\
-	__asm__(".weak alias");		\
-	__asm__(".equ alias, sym")
-
 #define __STRING(x)	#x
 #define __XSTRING(x)	__STRING(x)