Remove linking against unused GLEW on GNU/Linux.

[vanfanel]

GLEW does not seem to be used on GNU/Linux at all, so linking against it seems unnecessary: not linking against it has zero consequences, the engine builds and works without problems.

Not depending on GLEW makes SOH/LUS more easily portable to light GNU/Linux based desktop-less systems (building Xorg-less GLEW is possible but problematic), so this is all benefits.

[briaguya-ai]

what about

libultraship/src/graphic/Fast3D/gfx_opengl.cpp

Line 42 in d42849d

#include <GL/glew.h>

[vanfanel]

@briaguya-ai Yes, GLEW headers are apparently used instead of using SDL2 OpenGL headers.

We don't need to depend on GLEW just for headers that SDL2 already provides.

That's corrected in fdf95bd

[vanfanel]

@briaguya-ai Now everything builds without depending on GLEW headers.

[briaguya-ai]

you're changing too much here. keep it linux only for now. if you want to make a follow up PR removing GLEW for all platforms go for it, but this looks like a lot of copy-pasting with zero testing