buffer: move choice about using malloc closer to driver

This moves the decision about whether a buffer should be allocated using
malloc or not into cogl-buffer.c closer to the driver since it seem
there could be other driver specific factors that might also influence
this choice that we don't currently consider.

Reviewed-by: Neil Roberts <neil@linux.intel.com>

(cherry picked from commit 06d46f10bf755d3009c28904e616a0adb4586cf5)

cogl/cogl-index-buffer.c

@@ -45,18 +45,11 @@ CoglIndexBuffer *
 cogl_index_buffer_new (CoglContext *context, size_t bytes)
 {
   CoglIndexBuffer *indices = g_slice_new (CoglIndexBuffer);
-  CoglBool use_malloc;
-
-  if (!(context->private_feature_flags & COGL_PRIVATE_FEATURE_VBOS))
-    use_malloc = TRUE;
-  else
-    use_malloc = FALSE;
 
   /* parent's constructor */
   _cogl_buffer_initialize (COGL_BUFFER (indices),
                            context,
                            bytes,
-                           use_malloc,
                            COGL_BUFFER_BIND_TARGET_INDEX_BUFFER,
                            COGL_BUFFER_USAGE_HINT_INDEX_BUFFER,
                            COGL_BUFFER_UPDATE_HINT_STATIC);