Remove redundant keybindings for fuzzy finder

Some time in config history, CtrlP replaced FuzzyFinder. These were the
compatibility keybindings. However, CtrlP already has keys for these
commands.

Accept selection and open in vertical split: <c-v>
Accept selection and open in horizontal split: <c-s>

Let’s use those keys, so we can actually navigate the CtrlP window with
the standard vim home row keys!

Move up in the CtrlP selection window: <c-k>
Move down in the CtrlP selection window: <c-j>