Revert 250513 "Mojo: Add a Mutex class in public/utility."

broke linux build

> Mojo: Add a Mutex class in public/utility.
> 
> R=davemoore@chromium.org
> 
> Review URL: https://codereview.chromium.org/160053002

TBR=viettrungluu@chromium.org

Review URL: https://codereview.chromium.org/159893005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@250523 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 250523