GLES1: Reduce pressure on vertex input / varyings Typically, not all texture units are used. This change ensures no vertex input / varying is consumed when fewer than maximum textures are used. Bug: angleproject:6644 Change-Id: Iea0e35dc12ec4fcb342818786f307286bf7fc5bb Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/4081116 Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Cody Northrop <cnorthrop@google.com>