zlib: clean up some dead code

Cleanup unused `if 0'-ed functions, which have been dead since 2006
(commits 87c2ce3b ("lib/zlib*: cleanups") by Adrian Bunk and
4f3865fb

 ("zlib_inflate: Upgrade library code to a recent version")
by Richard Purdie):

 - zlib_deflateSetDictionary
 - zlib_deflateParams
 - zlib_deflateCopy
 - zlib_inflateSync
 - zlib_syncsearch
 - zlib_inflateSetDictionary
 - zlib_inflatePrime

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>