Make quiet installations possible

* util/build_scripts/doc-reference.py:
* util/build_scripts/generate-binding.py:
* util/meson_aux/extra-install-cmd.py: Don't print names of installed
files or other informative messages if the environment variable
MESON_INSTALL_QUIET is set.
It is set by "meson install --quiet" in Meson 0.54.0 and newer.