[shell] Revert interactiveness checks for eval

So that there's no error even when the scripts are mistakenly evaluated
in non-interactive sessions.

  bash -c 'eval "$(fzf --bash)"; echo done'
  zsh -c 'eval "$(fzf --zsh)"; echo done'

* https://github.com/junegunn/fzf/pull/3675#issuecomment-2044860901
* f103aa4753

shell/completion.bash

@@ -9,7 +9,7 @@
 # - $FZF_COMPLETION_TRIGGER (default: '**')
 # - $FZF_COMPLETION_OPTS    (default: empty)
 
-[[ $- =~ i ]] || return 0
+if [[ $- =~ i ]]; then
 
 
 # To use custom commands instead of find, override _fzf_compgen_{path,dir}
@@ -581,3 +581,5 @@ _fzf_setup_completion 'var'   export unset printenv
 _fzf_setup_completion 'alias' unalias
 _fzf_setup_completion 'host'  telnet
 _fzf_setup_completion 'proc'  kill
+
+fi