wifi adapter cleanspec

hidl-gen -L c++-adapter-main doesn't create a proper depfile or have
other dependencies listed, and so the intermediates aren't getting
updated. This only causes compilation problems when an interface is
removed, but may break tests when interfaces are added.

Fixes: 146227852
Test: reproduce error and use cleanspec to fix it
Change-Id: Ia2c5c30355eb2da9abbf32a9a000f41c3b4461b8