Use the new xb_builder_fixup_set_max_depth() for a pretty dramatic speedup

If we're fixing <component> then limit the traverse depth to 2 and save a huge
number of strcmp's when compiling a new binary blob.
1 job for wip/hughsie/libxmlb in 4 minutes and 45 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed #128708
build-gnome-software

00:04:45