d/rules: fix ubxtool to use python3 in the gpsd package (LP: #1878158)

package "gpsd" itself now has: Depends: netbase | systemd-sysv, lsb-base (>= 3.2-13), adduser (>= 3.34), libbluetooth3 (>= 4.91), libc6 (>= 2.29), libdbus-1-3 (>= 1.9.14), libusb-1.0-0 (>= 2:1.0.8), libgps26 (= 3.20-10), python2:any, python3:any (>= 3.5~), python3

Affects Ubuntu and Debian build.

# file $(dpkg -L gpsd) | grep -i pyth
/usr/bin/ubxtool: Python script, ASCII text executable

# head /usr/bin/ubxtool
#! /usr/bin/python2
# -*- coding: UTF-8

But it has further issues like:

$ ubxtool
ubxtool: failed to import gps, check PYTHONPATH

python3-gps isn't helping as it is python2 - and gpsd-clients (where ubxtool was before) is replacing python-gps but also not helping. There actually is NO python[2]-gps anymore that would help.

ubxtool was already made python3 compatible and fixed up in d/rules to have a proper python3 header.

With the moving around of binaries we fixed things that moved between gpsd-clients/gpsd-tools but the move of ubxtool to gpsd was missed and we need to fix things up on that again.

The commit in this MP gets ubxtool back into the former state which will then let gpsd have:

Depends: netbase | systemd-sysv, lsb-base (>= 3.2-13), adduser (>= 3.34), libbluetooth3 (>= 4.91), libc6 (>= 2.29), libdbus-1-3 (>= 1.9.14), libusb-1.0-0 (>= 2:1.0.8), libgps26 (= 3.20-10), python3:any (>= 3.5~), python3