mus: Remove the old client lib.

Remove the code for chrome-renderer that uses the old client-lib for mus.
Remove the old client-lib for mus since that is the only remaining use. A
subsequent CL will add a thin client-lib for chrome-renderer to use when
it runs as a mus-client (i.e. chrome is run with --use-mus-in-renderer).

TBR=jam@ and
    (trivial code update for deleted code)

Cr-Commit-Position: refs/heads/master@{#445423}
49 files changed