configure: Cleanup dbus variables

These are realistically not configurable by the end user and could be
provided as a runtime configuration if needed so that custom networkd
binaries are not needed for each different busname.

Configure variable substitution was kept to ensure the value is
consistent between all of the source files.

Change-Id: Ic6d50a80b48e2cfc07e48067089236010894e71b
Signed-off-by: William A. Kennington III <wak@google.com>
4 files changed