cifs: Remove unused functions

cifs_ses_find_chan() has been unused since commit
f486ef8e ("cifs: use the chans_need_reconnect bitmap for reconnect status")

cifs_read_page_from_socket() has been unused since commit
d08089f6 ("cifs: Change the I/O paths to use an iterator rather than a page list")

cifs_chan_in_reconnect() has been unused since commit
bc962159 ("cifs: avoid race conditions with parallel reconnects")

Remove them.

Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
Signed-off-by: Steve French <stfrench@microsoft.com>