R_SetupGL: remove some dead code (glGet call that stores GL_MODELVIEW_MATRIX into r_world_matrix, which is not used anywhere.)  The glGet calls was stalling the OpenGL pipeline.

git-svn-id: svn://svn.code.sf.net/p/quakespasm/code/trunk@1141 af15c1b1-3010-417e-b628-4374ebc0bcbd