LICENSE: Remove nvenc from the non-free section.

The headers are auto-detected by current FFmpeg.

LICENSE.md

@@ -112,7 +112,3 @@ unredistributable.
 The Fraunhofer FDK AAC and OpenSSL libraries are under licenses which are
 incompatible with the GPLv2 and v3. To the best of our knowledge, they are
 compatible with the LGPL.
-
-The NVENC library, while its header file is licensed under the compatible MIT
-license, requires a proprietary binary blob at run time, and is deemed to be
-incompatible with the GPL.