Strip redundant entries from .mailmap

Also prevent them from being reintroduced.

Change-Id: I4e16293c8185462b48e641f066d78449685e2854

.mailmap

 Adrian Grange <agrange@google.com>
-Adrian Grange <agrange@google.com> <agrange@agrange-macbookpro.roam.corp.google.com>
 Aℓex Converse <aconverse@google.com>
 Aℓex Converse <aconverse@google.com> <alex.converse@gmail.com>
 Alexis Ballier <aballier@gentoo.org> <alexis.ballier@gmail.com>
@@ -8,13 +7,11 @@ Deb Mukherjee <debargha@google.com>
 Erik Niemeyer <erik.a.niemeyer@intel.com> <erik.a.niemeyer@gmail.com>
 Guillaume Martres <gmartres@google.com> <smarter3@gmail.com>
 Hangyu Kuang <hkuang@google.com>
-Hangyu Kuang <hkuang@google.com> <hkuang@hkuang-macbookpro.roam.corp.google.com>
 Hui Su <huisu@google.com>
 Jacky Chen <jackychen@google.com>
 Jim Bankoski <jimbankoski@google.com>
 Johann Koenig <johannkoenig@google.com>
 Johann Koenig <johannkoenig@google.com> <johann.koenig@duck.com>
-Johann Koenig <johannkoenig@google.com> <johannkoenig@dhcp-172-19-7-52.mtv.corp.google.com>
 Johann Koenig <johannkoenig@google.com> <johann.koenig@gmail.com>
 John Koleszar <jkoleszar@google.com>
 Joshua Litt <joshualitt@google.com> <joshualitt@chromium.org>
@@ -33,4 +30,3 @@ Timothy B. Terriberry <tterribe@xiph.org> Tim Terriberry <tterriberry@mozilla.co
 Tom Finegan <tomfinegan@google.com>
 Tom Finegan <tomfinegan@google.com> <tomfinegan@chromium.org>
 Yaowu Xu <yaowu@google.com> <yaowu@xuyaowu.com>
-Yaowu Xu <yaowu@google.com> <yaowu@YAOWU2-W.ad.corp.google.com>

tools/gen_authors.sh

@@ -6,7 +6,7 @@ cat <<EOF
 # This file is automatically generated from the git commit history
 # by tools/gen_authors.sh.
 
-$(git log --pretty=format:"%aN <%aE>" | sort | uniq)
+$(git log --pretty=format:"%aN <%aE>" | sort | uniq | grep -v corp.google)
 Google Inc.
 The Mozilla Foundation
 The Xiph.Org Foundation