fcntl: remove unused VALID_UPGRADE_FLAGS

We currently do not maky use of this feature and should we implement
something like this in the future it's trivial to add it back.

Link: https://lore.kernel.org/r/20210528092417.3942079-2-brauner@kernel.org
Cc: Christoph Hellwig <hch@lst.de>
Cc: Aleksa Sarai <cyphar@cyphar.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Suggested-by: Richard Guy Briggs <rgb@redhat.com>
Reviewed-by: Richard Guy Briggs <rgb@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

include/linux/fcntl.h

@@ -12,10 +12,6 @@
 	 FASYNC	| O_DIRECT | O_LARGEFILE | O_DIRECTORY | O_NOFOLLOW | \
 	 O_NOATIME | O_CLOEXEC | O_PATH | __O_TMPFILE)
 
-/* List of all valid flags for the how->upgrade_mask argument: */
-#define VALID_UPGRADE_FLAGS \
-	(UPGRADE_NOWRITE | UPGRADE_NOREAD)
-
 /* List of all valid flags for the how->resolve argument: */
 #define VALID_RESOLVE_FLAGS \
 	(RESOLVE_NO_XDEV | RESOLVE_NO_MAGICLINKS | RESOLVE_NO_SYMLINKS | \