linker: remove APP_SMEM_SECTION() macro

Using this actually would result in a linker input section being
put between output sections which is not correct syntax.
We have never seen this simply because the generated ones would
be included instead of the in-tree ones. So remove this just in
case, instead of linker errors.

Signed-off-by: Daniel Leung <daniel.leung@intel.com>

include/linker/app_smem_aligned.ld

@@ -1,4 +1,3 @@
 /* SPDX-License-Identifier: Apache-2.0 */
 
-/* space holder  */
-APP_SMEM_SECTION()
+/* Empty file  */

include/linker/app_smem_unaligned.ld

@@ -1,4 +1,3 @@
 /* SPDX-License-Identifier: Apache-2.0 */
 
-/* space holder  */
-APP_SMEM_SECTION()
+/* Empty file */

include/linker/linker-defs.h

@@ -124,8 +124,6 @@
  * their shell commands are automatically initialized by the kernel.
  */
 
-#define APP_SMEM_SECTION() KEEP(*(SORT("data_smem_*")))
-
 #elif defined(_ASMLANGUAGE)
 
 /* Assembly FILES: declaration defined by the linker script */