Use libgl-devel to install OpenGL loader on Linux instead of CDTs

[traversaro]

This should be part of a much bigger cleanup of all the places in which we use OpenGL-related CDTs in ami-iit and robotology, but let's start from somewhere.

In a nutshell, now conda-forge packages the so-called libglvnd library, that is the loader library linked by the programs and that then loads the OpenGL libraries, so it is now sufficient to just install libgl-devel (or libegl-devel or other similar packages, depending on the library you actually use) instead of installing a lot of CDTs to compile a library that uses OpenGL.

Note that libgl-devel only install the GL loader library used to compile and link the library that uses OpenGL. To actually run a program that loads OpenGL, you need to install the OpenGL drivers, that are not packaged by conda-forge, and should instead be installed with the system package manager, for example:

• Debian/Ubuntu: sudo apt-get install libgl1-mesa-dri libglx-mesa0 libegl-mesa0
• Fedora/RHEL: sudo dnf install mesa-libGL mesa-libEGL mesa-dri-drivers

Related docs:

• https://conda-forge.org/docs/maintainer/maintainer_faq/#how-do-i-fix-the-libglso1-import-error