Removed double argument() calls

Removed double argument() calls

Some calls to the argument() function were made twice
because the emit() function didn't know what index to
use for each individual input. I added the function
arguments to the emit() function in order to solve that.

WebGL conformance tests pass.

Change-Id: I548b72cadf7247afd103b6be2ddfeaf39a995025
Reviewed-on: https://swiftshader-review.googlesource.com/4575
Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>