Adding array built-ins like gl_FragData and gl_LastFragData to the
symbol table with a name that included their size in brackets was
incorrect and unnecessary. Remove this. The array built-ins should only
be added with their proper name and with an array type.

Also refactor the code to reduce unnecessary repetition of conditions.
The previous version attempted to split the built-ins that had
dependencies on resources into their own part of the code, but this split
was not clearly defined and only made the code harder to follow and
prone to issues.

TEST=WebGL conformance tests

Change-Id: I7a77865a594864a22f3b566f9d3da1d0ead46466
Reviewed-on: https://chromium-review.googlesource.com/258751Reviewed-by: Nicolas Capens <capn@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Tested-by: Olli Etuaho <oetuaho@nvidia.com>