Remove our local modifications to sqlite's os_unix.c now that

      http://trac.webkit.org/changeset/68310 has landed.

They are no longer necessary, and are not used.

This brings our sqlite copy a little closer to the upstream version
and is a part of an effort to allow compiling with the system-provided sqlite.

BUG=50769, 22208
TEST=none

Review URL: http://codereview.chromium.org/3390032

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@60761 0039d316-1c4b-4281-b951-d872f2087c98