gnu-built: remove the useless sed

It will avoid a rebuilding when doing:
bash util/build-gnu.sh && bash util/run-gnu-test.sh   ../gnu/tests/rm/empty-inacc.sh

util/build-gnu.sh

@@ -102,8 +102,6 @@ for binary in $(./build-aux/gen-lists-of-programs.sh --list-progs); do
 done
 
 if test -f gnu-built; then
-    # Change the PATH in the Makefile to test the uutils coreutils instead of the GNU coreutils
-    sed -i "s/^[[:blank:]]*PATH=.*/  PATH='${UU_BUILD_DIR//\//\\/}\$(PATH_SEPARATOR)'\"\$\$PATH\" \\\/" Makefile
     echo "GNU build already found. Skip"
     echo "'rm -f $(pwd)/gnu-built' to force the build"
     echo "Note: the customization of the tests will still happen"