tests/check-gendoc

tests: remove last references to PYTHON3

This removes the last references to PYTHON3.

Differential Revision: https://phab.mercurial-scm.org/D12244

#!/bin/sh
HGENCODING=UTF-8
export HGENCODING

echo ".. -*- coding: utf-8 -*-" > gendoc.txt
echo "" >> gendoc.txt
LANGUAGE=$1 "$PYTHON" "$TESTDIR/../doc/gendoc.py" >> gendoc.txt 2> /dev/null || exit

echo "checking for parse errors"
"$PYTHON" "$TESTDIR/../doc/docchecker" gendoc.txt
"$PYTHON" "$TESTDIR/../doc/runrst" html gendoc.txt /dev/null