Fix large slowdown in rendering on some configurations.

Usage of GL_VERTEX_ARRAY client state apparently prevented OpenGL from using hardware acceleration on my computer (Macos 10.14 with an Intel GPU).
It is unclear how many people would be affected by this issue, but on my end it makes GLSL performance competitive with ARB again.

Reviewed By: vladislavbelov

Differential Revision: https://code.wildfiregames.com/D3900