Changelog: Drop duplicate NVENC entry

Found-by: NTimo Rothenpieler <timo@rothenpieler.org>
Signed-off-by: NMichael Niedermayer <michaelni@gmx.at>

Changelog

@@ -24,7 +24,6 @@ version <next>:
 - WebPAnimEncoder API when available for encoding and muxing WebP
 - Direct3D11-accelerated decoding
 - Support Secure Transport
-- NVIDIA NVENC-accelerated H.264 and HEVC encoding support
 
 
 version 2.6: