azure: remove unused Linux setup script

Since migrating to Docker containings for our build and test
infrastructure, we do not use the "setup-linux.sh" script anymore.
Remove it to avoid any confusion.

azure-pipelines/setup-linux.sh

-#!/bin/sh
-
-set -e
-set -x
-
-TMPDIR=${TMPDIR:-/tmp}
-
-if [ -z "$SKIP_APT" ]; then
-	apt-get update
-	apt-get -y install build-essential pkg-config clang cmake openssl libssl-dev libssh2-1-dev libcurl4-gnutls-dev openssh-server
-fi
-
-mkdir -p /var/run/sshd
-
-if [ "$MBEDTLS" ]; then
-	MBEDTLS_DIR=${MBEDTLS_DIR:-$(mktemp -d ${TMPDIR}/mbedtls.XXXXXXXX)}
-
-	git clone --depth 10 --single-branch --branch mbedtls-2.6.1 https://github.com/ARMmbed/mbedtls.git ${MBEDTLS_DIR}
-	cd ${MBEDTLS_DIR}
-
-	CFLAGS=-fPIC cmake -DENABLE_PROGRAMS=OFF -DENABLE_TESTING=OFF -DUSE_SHARED_MBEDTLS_LIBRARY=OFF -DUSE_STATIC_MBEDTLS_LIBRARY=ON .
-	cmake --build .
-
-	if [ -z "$SKIP_MBEDTLS_INSTALL" ]; then
-		make install
-	fi
-fi