doc: Remove old changelog fragments

doc/changes/auxiliary/mr.444.1.md

-u/vk: Remove unused vk_image struct, this is later recreated for the image
-allocator code.

doc/changes/auxiliary/mr.444.2.md

-u/vk: Add a new image allocate helper, this is used by the main compositor to
-create, export and import swapchain images.

doc/changes/auxiliary/mr.469.md

-u/vk: Rename `vk_create_semaphore_from_fd` to `vk_create_semaphore_from_native`

doc/changes/auxiliary/mr.493.1.md

-aux/ogl: Add a function to compute the texture target and binding enum for a given swapchain image creation info.

doc/changes/auxiliary/mr.493.md

----
-- mr.547
-- mr.581
----
-aux/android: New Android utility library added.

doc/changes/auxiliary/mr.574.1.md

-util: Tidy hand tracking header.

doc/changes/auxiliary/mr.574.2.md

-math: Fix doxygen warnings in vector headers.

doc/changes/compositor/mr.425.md

-compositor: Add support for alpha blending with premultiplied alpha.

doc/changes/compositor/mr.433.md

-compositor: Implement subimage rectangle rendering for quad layers.

doc/changes/compositor/mr.436.md

-compositor: Enable subimage rectangle rendering for projection layers.

doc/changes/compositor/mr.477.1.md

-compositor: Fix printing of current connected displays on nvidia when no whitelisted display is found.

doc/changes/compositor/mr.477.2.md

-compositor: Add env var to temporarily add display string to nvidia whitelist.

doc/changes/compositor/mr.479.md

-compositor and clients: Use a generic typedef to represent the platform-specific graphics buffer, allowing use of `AHardwareBuffer` on recent Android.

doc/changes/compositor/mr.481.md

-compositor: Check the protected content bit, and return a non-success code if it's set. Supporting this is optional in OpenXR, but lack of support must be reported to the application.

doc/changes/compositor/mr.495.md

-compositor: Implement cylinder layers.

doc/changes/compositor/mr.501.md

-main: Set the maximum layers supported to 16, we technically support more than
-16, but things get out of hand if multiple clients are running and all are using
-max layers.

doc/changes/compositor/mr.502.md

-main: Add code to check that a format is supported by the GPU before exposing.

doc/changes/compositor/mr.538.md

-compositor: Remove panotools and vive shaders from compositor.

doc/changes/compositor/mr.547.md

-Initial work on a port of the compositor to Android.

doc/changes/compositor/mr.566.md

-render: Implement equirect layer rendering.