Do not block OpenGL 2 when build for gles due to driver recommendation

Let's assume a user knows what she is doing when she selects kwin_gles
instead of kwin. Also in gles there is no fallback to OpenGL 1 possible
so blocking is not the proper solution in the first place.

BUG: 311712
FIXED-IN: 4.10 RC 2
REVIEW: 107824

scene_opengl.cpp

@@ -462,7 +462,9 @@ bool SceneOpenGL2::supported(OpenGLBackend *backend)
     }
     if (GLPlatform::instance()->recommendedCompositor() < OpenGL2Compositing) {
         kDebug(1212) << "Driver does not recommend OpenGL 2 compositing";
+#ifndef KWIN_HAVE_OPENGLES
         return false;
+#endif
     }
     if (options->isGlLegacy()) {
         kDebug(1212) << "OpenGL 2 disabled by config option";