Eliminate test_peg_generator redundant output

GitHub fields:

assignee = 'https://github.com/lysnikolaou'
closed_at = None
created_at = <Date 2020-10-19.17:27:28.030>
labels = ['interpreter-core', 'type-bug', 'tests', '3.10']
title = 'Eliminate test_peg_generator redundant output'
updated_at = <Date 2020-10-19.17:31:43.905>
user = 'https://github.com/terryjreedy'

bugs.python.org fields:

activity = <Date 2020-10-19.17:31:43.905>
actor = 'lys.nikolaou'
assignee = 'lys.nikolaou'
closed = False
closed_date = None
closer = None
components = ['Interpreter Core', 'Tests']
creation = <Date 2020-10-19.17:27:28.030>
creator = 'terry.reedy'
dependencies = []
files = []
hgrepos = []
issue_num = 42082
keywords = []
message_count = 2.0
messages = ['378970', '378971']
nosy_count = 3.0
nosy_names = ['terry.reedy', 'lys.nikolaou', 'pablogsal']
pr_nums = []
priority = 'normal'
resolution = None
stage = 'needs patch'
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue42082'
versions = ['Python 3.10']