ANDROID: Remove GKI ABI related padding from structures for microdroid

One of the cornerstones of GKI is that it preserves a stable ABI between
the kernel and vendor modules after the ABI is frozen. This ensures that
the kernel can be updated independently of the vendor modules. To do
this, space is reserved in certain data structures to account for
future changes that may require changes to the size of the structure
and break the ABI.

Microdroid kernels do not need to make this guarantee, so remove said
padding.

Bug: 432329937
Change-Id: Iec4afd7c748fe64c8dbd7770a333cbf4c6699f0e
Signed-off-by: Isaac J. Manjarres <isaacmanjarres@google.com>