Makefile: Remove duplicate gst_utils.py file from stbt-camera package
Makefile: Remove duplicate gst_utils.py file from stbt-camera package

This is already installed by the main stb-tester package. This was
caught by `test-deb.sh`:

> Unpacking stb-tester-camera (26-1) ...
> dpkg: error processing archive /tmp/stb-tester-camera_26-1_amd64.deb (--install):
>  trying to overwrite '/usr/lib/stbt/_stbt/gst_utils.py', which is also in package stb-tester 26-1

martynjarvis/stb-tester,martynjarvis/stb-tester,stb-tester/stb-tester,LewisHaley/stb-tester,stb-tester/stb-tester,martynjarvis/stb-tester,LewisHaley/stb-tester,LewisHaley/stb-tester,martynjarvis/stb-tester,LewisHaley/stb-tester,LewisHaley/stb-tester,martynjarvis/stb-tester,stb-tester/stb-tester,martynjarvis/stb-tester,martynjarvis/stb-tester,LewisHaley/stb-tester,stb-tester/stb-tester,LewisHaley/stb-tester