vo_opengl: remove redundant GL state initialization

All of these are already the defaults.

One exception is glDepthMask(), which is enabled by default. But if the
framebuffer has no depth buffer anyway, it shouldn't make a difference.

video/out/gl_video.c

@@ -2167,10 +2167,6 @@ static int init_gl(struct gl_video *p)
     check_gl_features(p);
 
     gl->Disable(GL_DITHER);
-    gl->Disable(GL_BLEND);
-    gl->Disable(GL_DEPTH_TEST);
-    gl->DepthMask(GL_FALSE);
-    gl->Disable(GL_CULL_FACE);
 
     gl->GenBuffers(1, &p->vertex_buffer);
     gl->BindBuffer(GL_ARRAY_BUFFER, p->vertex_buffer);