menuconfig: remove redundant info from RESERVED_LETTERS

first_alpha() checks only against lowercase characters anyway.

Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
menuconfig: allow j/k to move down/up the menu

Like in Vim.

Cc: Michal Marek <mmarek@suse.cz>
Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>