lib/zlib: drop EQUAL macro

lib/zlib: drop EQUAL macro

The macro is prehistoric, and only exists to help those readers who don't
know what memcmp() returns if memory areas differ.  This is pretty well
documented, so the macro looks excessive.

Now that the only user of the macro depends on DEBUG_ZLIB config, GCC
warns about unused macro if the library is built with W=2 against
defconfig.  So drop it for good.

Link: https://lkml.kernel.org/r/20250205212933.68695-1-yury.norov@gmail.com
Signed-off-by: Yury Norov <yury.norov@gmail.com>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Reviewed-by: Mikhail Zaslonko <zaslonko@linux.ibm.com>
Cc: Heiko Carsten <heiko.carstens@de.ibm.com>
Cc: Ilya Leoshkevich <iii@linux.ibm.com>
Cc: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>