Revert "Fix to restore bindings after switching to vi-mode"

This reverts commit b609aa0e -- this commit
was a bad idea, because it makes vi-mode very difficult to use. The default
`bindkey` keybindings are NOT MEANT to coexist with `bindkey -v` Vi mode;
that's why `bindkey -v` clears them in the first place! Restoring all of the
default keybindings after enabling Vi mode, the way the reverted commit did,
causes many collisions between those default keybindings that begin with ESC
and the command-mode-initiating ESC of Vi mode. See Issue 1438 of
robbyrussell/oh-my-zsh. If people have custom keybindings, they should create
them in their ~/.zshrc AFTER enabling the vi-mode plugin and sourcing
oh-my-zsh.sh.

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#	modified:   plugins/vi-mode/vi-mode.plugin.zsh
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