Cleanup code related to pbr wheel installation from git

Since I8e453110655c0e74ff81b4cdc796c4935c75a553, we don't generate pbr
wheels from git, so there is no need for this either.

Change-Id: I0c70735556d1da68924518b9deb13f4ed082a79d

tools/integration.sh

@@ -6,11 +6,6 @@ function mkvenv {
     rm -rf $venv
     virtualenv $venv
     $venv/bin/pip install -U pip wheel
-
-    # If a change to PBR is being tested, preinstall the wheel for it
-    if [ -n "$PBR_CHANGE" ] ; then
-        $venv/bin/pip install $pbrsdistdir/dist/pbr-*.whl
-    fi
 }
 
 function install_all_of_gr {