cifs: Remove cifs_truncate_page() as it should be superfluous

The calls to cifs_truncate_page() should be superfluous as the places that
call it also call truncate_setsize() or cifs_setsize() and therefore
truncate_pagecache() which should also clear the tail part of the folio
containing the EOF marker.

Further, smb3_simple_falloc() calls both cifs_setsize() and
truncate_setsize() in addition to cifs_truncate_page().

Remove the superfluous calls.

This gets rid of another function referring to struct page.

[Should cifs_setsize() also set inode->i_blocks?]

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Steve French <stfrench@microsoft.com>
Reviewed-by: Paulo Alcantara (Red Hat) <pc@manguebit.com>
cc: Matthew Wilcox <willy@infradead.org>
cc: linux-cifs@vger.kernel.org
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Steve French <stfrench@microsoft.com>