[bash-completion] Always backup existing completion definitions
[bash-completion] Always backup existing completion definitions

_fzf_completion_loaded is no longer checked. This change increases the
load time by a few milliseconds, but I can't think of a better way to
handle the issue.

Close #783.

wilywampa/fzf,tomfitzhenry/pkg-fzf,janlazo/fzf,wilywampa/fzf,wilywampa/fzf,infokiller/fzf,junegunn/fzf,janlazo/fzf,stuha/wbr-zsh,infokiller/fzf,infokiller/fzf,janlazo/fzf,tomfitzhenry/pkg-fzf,junegunn/fzf,junegunn/fzf,tomfitzhenry/pkg-fzf