widget binding: Remove an unnecessary layer of indirection.
widget binding: Remove an unnecessary layer of indirection.

The 'eval' was never needed, and the lack of proper quoting of the interpolated
variables caused issues, such as #278.

Fixes zsh-users/zsh-syntax-highlighting#278.

joshuarubin/dotfiles,danielshahaf/zsh-syntax-highlighting-debian,stuha/wbr-zsh,joshuarubin/dotfiles,x-way/zsh-syntax-highlighting,danielshahaf/zsh-syntax-highlighting,danielshahaf/zsh-syntax-highlighting,zsh-users/zsh-syntax-highlighting,psprint/zsh-syntax-highlighting,P71/zsh-syntax-highlighting,x-way/zsh-syntax-highlighting,phy1729/zsh-syntax-highlighting,joshuarubin/dotfiles,phy1729/zsh-syntax-highlighting,zsh-users/zsh-syntax-highlighting,P71/zsh-syntax-highlighting,m0vie/zsh-syntax-highlighting,danielshahaf/zsh-syntax-highlighting-debian,m0vie/zsh-syntax-highlighting,psprint/zsh-syntax-highlighting,joshuarubin/dotfiles