Skip DepsMutator on disabled modules

Dependencies of disabled modules may not have the right variations
for calling AddVariationDependencies, skip DepsMutator completely
on disabled modules.

Bug: 112707915
Test: m checkbuild
Test: prebuilts/build-tools/build-prebuilts.sh
Change-Id: I702e591437e5e6eb9f91f3b7eb32bacc4bd5d249