We would need to enable the wide lines feature to support non-unit line
widths. For now just disable the caps.

Bug: angleproject:2598
Bug: angleproject:2706
Change-Id: I0dd228fc2c357bdd9442c3d841be769987a53f72
Reviewed-on: https://chromium-review.googlesource.com/1127303Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>