gpu/internal/opengl,internal: move sRGB emulation to OpenGL driver

There is only one driver but several backends (EGL, WebGL).

Signed-off-by: Elias Naur <mail@eliasnaur.com>

gpu/headless/driver_test.go

@@ -174,7 +174,7 @@ func newDriver(t *testing.T) driver.Device {
 	if err != nil {
 		t.Fatal(err)
 	}
-	b.BeginFrame()
+	b.BeginFrame(image.Pt(1, 1))
 	t.Cleanup(func() {
 		b.EndFrame()
 		ctx.ReleaseCurrent()