Remove compatibility_matrix.9.xml from 'next' builds

This compatibility matrix has not be finalized or released yet, so it's
very important that releasing devices in the 'next' configuration don't
use its contents.

Test: m
Bug: 296930312
Change-Id: I843a24308a1653bff0b4842ff71e657304bea2c8
Merged-In: I843a24308a1653bff0b4842ff71e657304bea2c8