ffmpeg: remove shaderc

ffmpeng remove it in FFmpeg/FFmpeg@92f2e63

Author: zhongfly

packages/ffmpeg.cmake

@@ -33,7 +33,6 @@ ExternalProject_Add(ffmpeg
         libvpl
         libopenmpt
         libjxl
-        shaderc
         libplacebo
         libzvbi
         libaribcaption
@@ -100,7 +99,6 @@ ExternalProject_Add(ffmpeg
         --enable-libvpl
         --enable-libjxl
         --enable-libplacebo
-        --enable-libshaderc
         --enable-libzvbi
         --enable-libaribcaption
         ${ffmpeg_cuda}