IDLE: Remove annoying line in Shell sidebar

GitHub fields:

assignee = 'https://github.com/terryjreedy'
closed_at = None
created_at = <Date 2022-04-06.16:20:04.905>
labels = ['expert-IDLE', 'type-bug', '3.10']
title = 'Annoying white bar in IDLE (line 457 in sidebar.py)'
updated_at = <Date 2022-04-06.16:20:04.905>
user = 'https://github.com/antudic'

bugs.python.org fields:

activity = <Date 2022-04-06.16:20:04.905>
actor = 'antudic'
assignee = 'terry.reedy'
closed = False
closed_date = None
closer = None
components = ['IDLE']
creation = <Date 2022-04-06.16:20:04.905>
creator = 'antudic'
dependencies = []
files = []
hgrepos = []
issue_num = 47242
keywords = []
message_count = 1.0
messages = ['416883']
nosy_count = 2.0
nosy_names = ['terry.reedy', 'antudic']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue47242'
versions = ['Python 3.10']