Remove incorrect (and inappropriate) comment in dprintf_dnode

This comment seems to misunderstand the ## preprocessor token, which
does token concatenation.  It is not needed here, since we are
concatenating string literals, which is performed by putting the
literals next to each other.

Additionally, the comment uses offensive language.

Reviewed-by: Igor Kozhukhov <igor@dilos.org>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Tony Nguyen <tony.nguyen@delphix.com>
Signed-off-by: Matthew Ahrens <mahrens@delphix.com>
Closes openzfs#8698
Closes openzfs#8699

include/sys/dnode.h

@@ -589,11 +589,6 @@ extern dnode_stats_t dnode_stats;
 
 #ifdef ZFS_DEBUG
 
-/*
- * There should be a ## between the string literal and fmt, to make it
- * clear that we're joining two strings together, but that piece of shit
- * gcc doesn't support that preprocessor token.
- */
 #define	dprintf_dnode(dn, fmt, ...) do { \
 	if (zfs_flags & ZFS_DEBUG_DPRINTF) { \
 	char __db_buf[32]; \