Remove doc/old/nommu-notes.txt

UCLINUX is dead and it's support has been removed from LTP.

Although Documentation/admin-guide/mm/nommu-mmap.rst still exists in
kernel tree, there is nobody really using it.

Signed-off-by: Petr Vorel <[email protected]>
Reviewed-by: Cyril Hrubis <[email protected]>

Author: pevik