There are no longer @@ QUALIFIER and or @@ LAYOUT markers.  Only @@
XFB-DECL @@ and @@ XFB-OUT @@ markers remain, which are now replaced
with simple string manipulation.

Bug: angleproject:3394
Change-Id: I9c1883458d9de3ea59ac08aae57a7c8985e7afbe
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2012741
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Tim Van Patten <timvp@google.com>