Clean up division fast paths in Objects/longobject.c

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2016-09-10.10:46:13.057>
labels = ['performance']
title = 'Clean up division fast paths in Objects/longobject.c'
updated_at = <Date 2017-07-22.10:09:56.204>
user = 'https://github.com/mdickinson'

bugs.python.org fields:

activity = <Date 2017-07-22.10:09:56.204>
actor = 'mark.dickinson'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = []
creation = <Date 2016-09-10.10:46:13.057>
creator = 'mark.dickinson'
dependencies = []
files = ['44528']
hgrepos = []
issue_num = 28060
keywords = ['patch']
message_count = 6.0
messages = ['275618', '275619', '275675', '275679', '298843', '298845']
nosy_count = 3.0
nosy_names = ['mark.dickinson', 'pitrou', 'serhiy.storchaka']
pr_nums = []
priority = 'normal'
resolution = None
stage = 'commit review'
status = 'open'
superseder = None
type = 'performance'
url = 'https://bugs.python.org/issue28060'
versions = ['Python 3.6']