cpu/lm4f120: Remove stub cpuid

NVIC_CPUID is not a unique device ID, it is the Cortex-M core family ID.

boards/ek-lm4f120xl/Makefile.features

@@ -1,6 +1,5 @@
 # Put defined MCU peripherals here (in alphabetical order)
 FEATURES_PROVIDED += periph_adc
-FEATURES_PROVIDED += periph_cpuid
 FEATURES_PROVIDED += periph_gpio
 FEATURES_PROVIDED += periph_timer
 FEATURES_PROVIDED += periph_uart

cpu/lm4f120/periph/cpuid.c

@@ -1,29 +0,0 @@
-/*
- * Copyright (C) 2015 Rakendra Thapa <rakendrathapa@gmail.com>
- *
- * This file is subject to the terms and conditions of the GNU Lesser
- * General Public License v2.1. See the file LICENSE in the top level
- * directory for more details.
- */
-
-/**
- * @addtogroup      cpu_lm4f120
- * @{
- *
- * @file
- * @brief           Low-level CPUID driver implementation
- *
- * @author          Rakendra Thapa <rakendrathapa@gmail.com>
- *
- * @}
- */
-
-#include <string.h>
-
-#include "cpu.h"
-#include "periph/cpuid.h"
-
-void cpuid_get(void *id)
-{
-    memcpy(id, (void *)(NVIC_CPUID), CPUID_LEN);
-}