azure-pipeline: stop hard-coding apt-get calls

We have `ci/install-dependencies.sh` for that. Incidentally, this avoids
the following error in the linux-* jobs:

    The following packages have unmet dependencies:
    git-email : Depends: git (< 1:2.25.1-.) but 1:2.35.1-0ppa1~ubuntu20.04.1 is to be installed
	  Recommends: libemail-valid-perl but it is not going to be installed

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

azure-pipelines.yml

@@ -303,9 +303,6 @@ jobs:
   - bash: |
        test "$GITFILESHAREPWD" = '$(gitfileshare.pwd)' || ci/mount-fileshare.sh //gitfileshare.file.core.windows.net/test-cache gitfileshare "$GITFILESHAREPWD" "$HOME/test-cache" || exit 1
 
-       sudo apt-get update &&
-       sudo apt-get -y install git gcc make libssl-dev libcurl4-openssl-dev libexpat-dev tcl tk gettext git-email zlib1g-dev apache2-bin &&
-
        export CC=clang || exit 1
 
        ci/install-dependencies.sh || exit 1
@@ -342,10 +339,6 @@ jobs:
   - bash: |
        test "$GITFILESHAREPWD" = '$(gitfileshare.pwd)' || ci/mount-fileshare.sh //gitfileshare.file.core.windows.net/test-cache gitfileshare "$GITFILESHAREPWD" "$HOME/test-cache" || exit 1
 
-       sudo add-apt-repository ppa:ubuntu-toolchain-r/test &&
-       sudo apt-get update &&
-       sudo apt-get -y install git gcc make libssl-dev libcurl4-openssl-dev libexpat-dev tcl tk gettext git-email zlib1g-dev apache2 language-pack-is git-svn gcc-8 || exit 1
-
        ci/install-dependencies.sh || exit 1
        ci/run-build-and-tests.sh || {
            ci/print-test-failures.sh