musca_b1: Remove device-specific virtual NVIC

Use instead the general TF-M v8-M virtual NVIC which will be added in
the commit that replaces Mbed PSA with TF-M PSA:
features/FEATURE_PSA/TARGET_TFM/TARGET_TFM_V8M/src/cmsis_nvic_virtual.c

targets/TARGET_ARM_SSG/TARGET_MUSCA_B1/device/cmsis_nvic_virtual.c

@@ -1,25 +0,0 @@
-/*
- * Copyright (c) 2020 Arm Limited
- *
- * SPDX-License-Identifier: Apache-2.0
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-#include "cmsis_nvic_virtual.h"
-#include "psa/lifecycle.h"
-
-void NVIC_SystemReset(void)
-{
-    mbed_psa_system_reset();
-}