If you're looking for the files vulkan_ext.[ch] in this directory, they have been removed. There were two significant problems with these simple wrappers.
First, vulkan_ext exported all extension entrypoints. However, the Vulkan loader also exports entrypoints for the window system integration extensions. If someone tried to compile a project and link it to both the loader and vulkan_ext, they would get a bunch of redefined symbols. This linking error is difficult to work around, because vulkan_ext does not have an easy method of disabling the entrypoints at compile time. It is possible to remove these entrypoints when generating vulkan_ext, but even then you have to manually compile a list of every single extension to be disabled.
Second, each entrypoint is only stored once, regardless of how many instances or devices are created. This means that attempting to use multiple instances or devices in parallel can result in one device calling function pointers that are only valid on the other device, which will crash. You may be able to work around this by never initializing the device dispatch (vkExtInitDevice), but we haven't tried this.
It is still possible to retrieve the last versions of these files in the Github KhronosGroup/Vulkan-Docs repository from the ‘v1.1.75’ release tag. It is also possible to regenerate them from ../../xml/vk.xml, although we are no longer maintaining the generator code and it may eventually stop working correctly. See README.adoc and the extloader Makefile target in that directory.