fja_checker: Drop .parser from imports

fja_checker/__main__.py

 import lib.reg as reg
 import lib.cfl as cfl
-from lib.parsing.parser import Parser, ParsingError
+from lib.parsing import Parser, ParsingError
 from lib.checker import get_task, dfa_transform, nfa_transform, check_task, check_empty, check_alphabets, exit_correct, exit_incorrect
 import sys
 import signal