ChromeOS: Remove Profile::IsLoginProfile.

IsLoginProfile is based on ProfileHelper::IsSigninProfile.
There is no obvious/good reason why IsLoginProfile is additionally required. Even worse, IsLoginProfile is implemented by every subclass of Profile and is inconsistent to ProfileHelper::IsSigninProfile and to Profile::GetPath().

BUG=312660
(For Fake-/TestingProfile)

R=davemoore@google.com, nkostylev@chromium.org
TBR=ben@chromium.org

Review URL: https://codereview.chromium.org/47923016

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@233263 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 233263