gen_esp32part.py: use Python3

dist/tools/esptool/gen_esp32part.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 #
 # ESP32 partition table generation tool
 #
@@ -20,7 +20,6 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
-from __future__ import print_function, division
 import argparse
 import os
 import re