Also remove the TSymbol copy constructor which is not used.

BUG=angle:836

Change-Id: I4f35f554c90d01dc2132d244a1974d9a8dc89bbd
Reviewed-on: https://chromium-review.googlesource.com/231231Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Shannon Woods <shannonwoods@chromium.org>
Tested-by: Geoff Lang <geofflang@chromium.org>