vulkan: Move implementor's guide to s.a.c.

Contents have been at
    https://source.android.com/devices/graphics/implement-vulkan
for a while now. Removing the one here so we have a canonical source
and don't have to worry about propagating changes from one to the
other.

Test: n/a
Bug: 78347023
Change-Id: I5e65d0aef530a761c75efe999ade8c44bc421a9e