[cogl] Force Cogl to always use the client side matrix stack

Previously we only used the Cogl matrix stack API for indirect contexts, but
it's too costly to keep on requesting modelview matrices from GL (for
logging in the journal) even for direct rendering.

I also experimented with a patch for mesa to improve performance and
discussed this with upstream, but we agreed to consider the GL matrix API
essentially deprecated.  (For reference the GLES 2 and GL 3 specs have
removed the matrix APIs)

common/cogl-current-matrix.c

@@ -320,8 +320,10 @@ _cogl_current_matrix_state_init (void)
   ctx->matrix_mode = COGL_MATRIX_MODELVIEW;
   ctx->modelview_stack = NULL;
 
+#if 0
   if (ctx->indirect ||
       cogl_debug_flags & COGL_DEBUG_FORCE_CLIENT_SIDE_MATRICES)
+#endif
     {
       ctx->modelview_stack =
         _cogl_matrix_stack_new ();