Always add legacy DeviceConfigService to ServiceManager

Now that we are able to handover shell commands from the legacy (i.e.
platform-provided) DeviceConfigService to the mainline-module-provided
service, we always add the legacy service and it can decide to hand over
the command to the mainline service when appropriate.

Bug: 263955152

Test: manual because logic is behind feature flags
Change-Id: I1ef0235e3a262b5cd5cb8b5f6c40fe1fc0202e53