FreeBSD: Fix the build on FreeBSD 12

It was broken for several reasons:
* VOP_UNLOCK lost an argument in 13.0.  So OpenZFS should be using
  VOP_UNLOCK1, but a few direct calls to VOP_UNLOCK snuck in.
* The location of the zlib header moved in 13.0 and 12.1.  We can drop
  support for building on 12.0, which is EoL.
* knlist_init lost an argument in 13.0.  OpenZFS change 9d0887402b
  assumed 13.0 or later.
* FreeBSD 13.0 added copy_file_range, and OpenZFS change 67a1b03791
  assumed 13.0 or later.

Sponsored-by: Axcient
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Signed-off-by: Alan Somers <asomers@gmail.com>
Closes #15551

module/os/freebsd/spl/spl_zlib.c

@@ -29,11 +29,7 @@
 #include <sys/kmem.h>
 #include <sys/kmem_cache.h>
 #include <sys/zmod.h>
-#if __FreeBSD_version >= 1300041
 #include <contrib/zlib/zlib.h>
-#else
-#include <sys/zlib.h>
-#endif
 #include <sys/kobj.h>
 
 
@@ -87,11 +83,7 @@ zlib_inflateInit(z_stream *stream)
 static int
 zlib_inflate(z_stream *stream, int finish)
 {
-#if __FreeBSD_version >= 1300024
 	return (inflate(stream, finish));
-#else
-	return (_zlib104_inflate(stream, finish));
-#endif
 }