Revert 247473 "PPAPI: Implement PPB_FileMapping on POSIX"

> PPAPI: Implement PPB_FileMapping on POSIX
> 
> BUG=83774
> R=bbudge@chromium.org
> 
> Review URL: https://codereview.chromium.org/69663002

TBR=dmichael@chromium.org

Review URL: https://codereview.chromium.org/144383006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247477 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 247477