Clean up TSymbolTable entry points TSymbolTable API can be cleaned up further now that we have separate logic for inserting builtins and user-defined symbols. BUG=angleprojec:2267 TEST=angle_unittests Change-Id: I7a228891ecdf4696e50868b9e7dfc2a50b5d8e92 Reviewed-on: https://chromium-review.googlesource.com/941301 Commit-Queue: Olli Etuaho <oetuaho@nvidia.com> Reviewed-by: Corentin Wallez <cwallez@chromium.org>