Need to rename kVar* variables to just var

Bug: angleproject:3823
Change-Id: I34b9f4eec4ee7829d47dcac2f06f1acc6b35f867
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1758601Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Clemen Deng <clemendeng@google.com>