Remove fake client creation from DBusClients' Create() functions.

The DBusClient interfaces shouldn't provide functionality related to testing code (like Stubs/fake implementations).
Instead fake clients are now directly created without relying on the static Create() functions. The now unused DBusClientImplementationType argument of the Create() functions could be removed.

BUG=275286
R=satorux@chromium.org

Review URL: https://codereview.chromium.org/91413002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@238330 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 238330