Drop section describung now unneeded workarounds for BSD

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

doc/general.texi

@@ -789,14 +789,6 @@ to configure.
 BSD make will not build FFmpeg, you need to install and use GNU Make
 (@file{gmake}).
 
-@subsubsection FreeBSD, DragonFly BSD
-
-These systems will not compile out-of-the-box due to broken system headers.
-Passing @code{--extra-cflags=-D__BSD_VISIBLE} to configure will work
-around the problem. This may have unexpected sideeffects, so use it at
-your own risk. If you care about FreeBSD, please make an attempt at
-getting the system headers fixed.
-
 @subsection (Open)Solaris
 
 GNU Make is required to build FFmpeg, so you have to invoke (@file{gmake}),