Delete wrapper API ConvertToI420 for YUV conversion to I420

Directly use the libyuv API for YUV conversion to I420

Bug: None
Change-Id: Iea6e8fa8f7179c800ea850305170002398cb00dc
Reviewed-on: https://webrtc-review.googlesource.com/17260
Commit-Queue: Niels Moller <nisse@webrtc.org>
Reviewed-by: Åsa Persson <asapersson@webrtc.org>
Reviewed-by: Alex Glaznev <glaznev@webrtc.org>
Reviewed-by: Niels Moller <nisse@webrtc.org>
Reviewed-by: Magnus Jedvert <magjed@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20681}
diff --git a/AUTHORS b/AUTHORS
index 285cde4..3a73bd6 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -28,6 +28,7 @@
 Jiawei Ou <jiawei.ou@gmail.com>
 Jie Mao <maojie0924@gmail.com>
 Luke Weber <luke.weber@gmail.com>
+Mallikarjuna Rao V <vm.arjun@samsung.com>
 Manish Jethani <manish.jethani@gmail.com>
 Martin Storsjo <martin@martin.st>
 Matthias Liebig <matthias.gcode@gmail.com>