YUV 411 is very uncommon format.  Remove support.

Update documentation to reflect that 411 is deprecated.

Simplify tests for YUV to only test with the new side by side YUV but keep old 3 plane test around with a macro for now.

BUG=libyuv:645
R=kjellander@chromium.org

Review URL: https://codereview.chromium.org/2406123002 .

The conversion from NV12 and other Bi or Tri planar formats, differs only in the UV handling.  The helper function supports passing a NULL for the dst_y channel indicating you only want to do the UV conversion.

TBR=harryjin@google.com
TEST=LibYUVConvertTest.NV12ToI420_NullY (601 ms)
BUG=libyuv:626

Review URL: https://codereview.chromium.org/2276703002 .

This is based on today's content at
https://code.google.com/p/libyuv/w/list

BUG=chromium:587193

Review URL: https://codereview.chromium.org/1703653002 .