tmux: bump to version 2.2

tmux: bump to version 2.2

- remove patch already upstream 0001-remove-use-of-sys-cdefs.h.patch
https://github.com/tmux/tmux/commit/7b085136a7291cbcdfcc53182fbd13aaca70306e
- add new dependency on BR2_USE_WCHAR (version 2.2 uses mbtowc())
- add new dependency on locale support
- add note to help text about the need of a working UTF-8 locale
- also rewrap help text to 72 characters

Signed-off-by: Ricardo Martincoski <ricardo.martincoski@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>