vfs: remove externs from fs.h on functions modified by i_ino widening

vfs: remove externs from fs.h on functions modified by i_ino widening

Christoph says, in response to one of the patches in the i_ino widening
series, which changes the prototype of several functions in fs.h:

    "Can you please drop all these pointless externs while you're at it?"

Remove extern keyword from functions touched by that patch (and a few
that happened to be nearby). Also add missing argument names to
declarations that lacked them.

Suggested-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Link: https://patch.msgid.link/20260307-iino-u64-v2-1-a1a1696e0653@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>