locks: remove LOCK_MAND flock lock support

As best I can tell, the logic for these has been broken for a long time
(at least before the move to git), such that they never conflict with
anything. Also, nothing checks for these flags and prevented opens or
read/write behavior on the files. They don't seem to do anything.

Given that, we can rip these symbols out of the kernel, and just make
flock(2) return 0 when LOCK_MAND is set in order to preserve existing
behavior.

Cc: Matthew Wilcox <willy@infradead.org>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Jeff Layton <jlayton@kernel.org>

include/uapi/asm-generic/fcntl.h

@@ -181,6 +181,10 @@ struct f_owner_ex {
 				   blocking */
 #define LOCK_UN		8	/* remove lock */
 
+/*
+ * LOCK_MAND support has been removed from the kernel. We leave the symbols
+ * here to not break legacy builds, but these should not be used in new code.
+ */
 #define LOCK_MAND	32	/* This is a mandatory flock ... */
 #define LOCK_READ	64	/* which allows concurrent read operations */
 #define LOCK_WRITE	128	/* which allows concurrent write operations */