delete unnecessary imports

evalweb/evalweb.py

-from flask import Blueprint, flash, render_template, request
+from flask import Blueprint, render_template, request
 from flask_wtf import FlaskForm
 from wtforms import RadioField
 import sys

lib/reg.py

-from typing import Set, Tuple, Dict, Union
-from lib.common import Terminal, Nonterminal, State, Character, Eps, Emptyset
+from typing import Set
+from lib.common import Terminal, Nonterminal, Eps
 from lib.grammars import RegGrammar, CFG
 from lib.dfa import DFA
 from lib.nfa import NFA