[build] Remove obsolete gn flag
[build] Remove obsolete gn flag

Bug: chromium:1164276
Change-Id: I2c7ed46ddf5ed027d316bc02f76a957b29101734
Reviewed-on: https://chromium-review.googlesource.com/c/libyuv/libyuv/+/2622076
Reviewed-by: Frank Barchard <52415189a3f67d375195cbbb6fdb1f1759498e57@chromium.org>

lemenkov/libyuv,lemenkov/libyuv,lemenkov/libyuv,lemenkov/libyuv