They've been replaced by using constructor nodes, so any code handling conversion operators
can be removed.

BUG=15415045

Change-Id: Ibf277f3014800b6e9503d65f102f8d8b6013a2d7
Reviewed-on: https://swiftshader-review.googlesource.com/1114Reviewed-by: Nicolas Capens <nicolascapens@google.com>