doc/general.texi: remove note about regressed AviSynth+ header

It's been fixed both AviSynth+-side and locally.

doc/general.texi

@@ -51,19 +51,6 @@ For Windows, supported AviSynth variants are
 For Linux and OS X, the supported AviSynth variant is
 @url{https://github.com/avxsynth/avxsynth, AvxSynth}.
 
-@float NOTE
-There is currently a regression in AviSynth+'s @code{capi.h} header as of
-October 2016, which interferes with the ability for builds of FFmpeg to use
-MSVC-built binaries of AviSynth. Until this is resolved, you can make sure
-a known good version is installed by checking out a version from before
-the regression occurred:
-
-@code{git clone -b MT git://github.com/AviSynth/AviSynthPlus.git @*
-cd AviSynthPlus @*
-git checkout -b oldheader b4f292b4dbfad149697fb65c6a037bb3810813f9 @*
-make install PREFIX=/install/prefix}
-@end float
-
 @float NOTE
 AviSynth and AvxSynth are loaded dynamically.  Distributors can build FFmpeg
 with @code{--enable-avisynth}, and the binaries will work regardless of the