do not install zbuff.h

this API is deprecated, for a loong time now,
all related symbols will be removed in a future version (likely v1.5.0)
and the header file `zbuff.h` doesn't compile from `include/` anyway,
because it needs to be positioned one directory below `zstd.h`.

Also removed `cover.h` from `cmake` installer,
as it should have never been part of this list to begin with.

build/meson/lib/meson.build

@@ -127,6 +127,5 @@ pkgconfig.generate(libzstd,
   url: 'http://www.zstd.net/')
 
 install_headers(join_paths(zstd_rootdir, 'lib/zstd.h'),
-  join_paths(zstd_rootdir, 'lib/deprecated/zbuff.h'),
   join_paths(zstd_rootdir, 'lib/dictBuilder/zdict.h'),
   join_paths(zstd_rootdir, 'lib/common/zstd_errors.h'))