Remove --disable-restore-session-state.

The feature has been stable a long time now.

(This CL is part of the command line flag removal effort.)

BUG=

Review URL: https://codereview.chromium.org/190603002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@255682 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 255682