Do not install doc build tools in GitLab CI jobs

As documentation building utilities are now all included in operating
system images used in GitLab CI, do not install them in each "docs" CI
job any more.

.gitlab-ci.yml

@@ -471,9 +471,6 @@ docs:
   before_script:
     - test -w "${CCACHE_DIR}" && export PATH="/usr/lib/ccache:${PATH}"
     - test -n "${OOT_BUILD_WORKSPACE}" && mkdir "${OOT_BUILD_WORKSPACE}" && cd "${OOT_BUILD_WORKSPACE}"
-    - apt -yqqq update
-    - apt -yqqq dist-upgrade
-    - apt -yqqq install texlive-full texlive-xetex latexmk xindy
   script:
     - *configure
     - make -j${BUILD_PARALLEL_JOBS:-1} -k maintainer-clean V=1