vulkan: Update templates for generated extensions

When the swapchain extensions were added to the API file, only
the libvulkan/get_proc_addr.cpp template was updated. This change
updates the remaining templates, so that when used they generate the
appropriate output with the new API file:

- libvulkan/entry.cpp: Remove hardcoded extension entry points, now
  that they're autogenerated.
- nulldrv/null_driver_gen.cpp: Exclude all extension entry points;
  this only works because the API currently only includes entry points
  implemented by the loader. Eventually we'll want to replace this
  with an extension blacklist.

Change-Id: Id6ea11fb739390d8262fa5ce77c213fbbdeb0148
(cherry picked from commit 1d40de6ecdd74c47ebd40fadd5926cc2984cc91c)