meson: skip installation of GLVND-provided headers

Fixes: 93df862b ("meson: re-add incorrect pkg-config files with GLVND for backward compatibility")
Closes: https://gitlab.freedesktop.org/mesa/mesa/issues/1846


Signed-off-by: Eric Engestrom <eric.engestrom@intel.com>
Reviewed-by: Dylan Baker <dylan@pnwbakers.com>
(cherry picked from commit 34ba363a)