Remove more 3rd party sources from release tarballs

[jlblancoc]

• [x] 3rdparty/googletest/* -> libgtest-dev, libgmock-dev ==> Done via 161d16c71fd1fcc21bd0d7d3934b84b850b48528
• [x] 3rdparty/nanogui/ext/nanovg/example/Roboto-*.ttf -> fonts-roboto ==> Done via uscan d/copyright Files-Excluded since those files are not used at all in mrpt builds.
• [x] 3rdparty/glew/* -> libglew-dev ==> Via Files-Excluded too. Used for Windows builds exclusively.
• [x] 3rdparty/freeglut/* -> freeglut3-dev ==> Via Files-Excluded too. Already not used by cmake if the freeglut3-dev is found.
• [x] 3rdparty/glext/* -> libgl-dev ==> Via Files-Excluded too. pkg already provided by build-dep libglu1-mesa-dev.
• [x] libs/math/src/CSparse/ -> libsuitesparse-dev ==> Via Files-Excluded too. Not used if libsuitesparse-dev is found (already a build-dep).

As suggested by @jspricke .

Alternatives (on the fly download / clone?) should be added for Windows users, I guess...

[jspricke]

Alternatives (on the fly download / clone?) should be added for Windows users, I guess...

There are package managers for Windows, maybe they could provide the dependencies?

[jlblancoc]

@jspricke well, thanks to the d/copyright Files-Excluded feature, it was far easier than expected... only one patch needed for gtest, the rest are handled via d/copyright.