According to the OpenGL ES 1.1 spec, remove the conditions
of glOrtho validation that n and f must be positive.

Bug: angleproject:4281
Change-Id: I644a25408a026ce87211f2203b8e8203eeaf69bd
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2067002Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>