# coding: utf-8
import re
f = open('f.txt').read().decode('utf-8')
pat = ur'([{0}])[{0}]+'.format(u'bcdfghjklmnpqrstvwxzбвгджзйклмнпрстфхцчшщъь')
output = re.sub(pat, r'\1', f, flags=re.I | re.U)
open('f_new.txt','w').write(output.encode('utf-8'))