remove unnecessary omz plugin

The deficiency with multi-line prompts in vi-mode have now been resolved.

zsh/omz-custom/plugins/vi-mode/vi-mode.plugin.zsh

@@ -1,27 +0,0 @@
-#
-# This plugin is modified to work better with multiline prompts. The problem
-# and solutions are described in
-# https://github.com/robbyrussell/oh-my-zsh/pull/597
-# (basically, zle-line-init is taken out)
-#
-function zle-keymap-select {
-  zle reset-prompt
-}
-
-zle -N zle-keymap-select
-
-bindkey -v
-
-# if mode indicator wasn't setup by theme, define default
-if [[ "$MODE_INDICATOR" == "" ]]; then
-  MODE_INDICATOR="%{$fg_bold[red]%}<%{$fg[red]%}<<%{$reset_color%}"
-fi
-
-function vi_mode_prompt_info() {
-  echo "${${KEYMAP/vicmd/$MODE_INDICATOR}/(main|viins)/}"
-}
-
-# define right prompt, if it wasn't defined by a theme
-if [[ "$RPS1" == "" && "$RPROMPT" == "" ]]; then
-  RPS1='$(vi_mode_prompt_info)'
-fi