Cleanup legacy flags and switches

kLoginScreen
kLoginScreenSize

kAshBootAnimationFunction2
kAshBootAnimationFunction3
kAshDisableBootAnimation2
+ related flags

See also https://gerrit.chromium.org/gerrit/#/c/56735/

BUG=244224
TEST=compiles, existing browser_tests and autotests work
NOTRY=true

Review URL: https://chromiumcodereview.appspot.com/16105005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@202646 0039d316-1c4b-4281-b951-d872f2087c98
17 files changed