Rename Kotlin util files to not include the Kt suffix

Callers don't care what language the utilities are written in

This is a partial cherry-pick of the change in the packages/Tethering,
tests/net/common, tests/net/integration, wifi/tests directories. Other
tests cannot be kept in sync as the latest versions verify platform
functionalities that do not exist in the module branch, so disabling
them is less time-consuming than always resolving merge conflicts.

Test: builds
Merged-In: Ie212144f36c50db223c05f3fcb6bad745842cb5e
Change-Id: Ie212144f36c50db223c05f3fcb6bad745842cb5e