EC_POINT_set_affine_coordinates_GFp already rejects coordinates which
are out of range. There's no need to double-check.
Change-Id: Id1685355c555dda66d2a14125cb0083342f37e53
Reviewed-on: https://boringssl-review.googlesource.com/24688
Reviewed-by: Adam Langley <agl@google.com>