Remove cppcheck from CI, add to tools/

We don't enforce cppcheck through the CI, although it's there since
years. It runs on Ubuntu 18/20, so it's old. For folks, it's likely not
discoverable on how to run it locally. Let's make a fresh start.

This removes cppcheck from all CI-related code. Instead, it adds it
under tools/cppcheck/, including documentation on how to run it locally,
bare-matel or in docker.

Signed-off-by: Robert Schmidt <robert.schmidt@openairinterface.org>

ci-scripts/docker/Dockerfile.cppcheck.xenial

@@ -1,41 +0,0 @@
-# SPDX-License-Identifier: LicenseRef-CSSL-1.0
-
-#---------------------------------------------------------------------
-#
-# Dockerfile for the Open-Air-Interface BUILD service
-#   Valid for Ubuntu 22.04
-#
-#---------------------------------------------------------------------
-FROM ubuntu:xenial AS oai-cppcheck
-
-
-ENV DEBIAN_FRONTEND=noninteractive
-
-RUN apt-get update && \
-    apt-get upgrade --yes && \
-    apt-get install --yes \
-       build-essential \
-       vim \
-       cppcheck
-
-WORKDIR /oai-ran
-COPY . .
-
-WORKDIR /oai-ran/common/utils/T
-RUN make
-
-WORKDIR /oai-ran
-RUN mkdir -p cmake_targets/log && \
-    cppcheck --enable=warning --force --xml --xml-version=2 \
-        --inline-suppr \
-        -i openair1/PHY/CODING/nrLDPC_decoder/nrLDPC_decoder.c \
-        --suppressions-list=ci-scripts/cppcheck_suppressions.list \
-        -I common/utils \
-        -I openair3/NAS/COMMON/UTIL \
-        -j`nproc` . 2> cmake_targets/log/cppcheck.xml 1> cmake_targets/log/cppcheck_build.txt
-
-RUN grep -E -c 'severity="error' cmake_targets/log/cppcheck.xml
-
-RUN grep -E -c 'severity="warning' cmake_targets/log/cppcheck.xml
-
-RUN cat cmake_targets/log/cppcheck.xml