[fish] drop interactiveness-checks support for fish versions < 3.4.0

This improves commit 5cb5bbd by just returning
from the script in case it’s sourced from a non-interactive shell, rather then
using an `if`-block to not execute any further code (which is error prone, in
case code gets accidentally added outside the `if`, and also less readable).

This removes support for fish versions < 3.4.0, which should now no longer be
used.

Signed-off-by: Christoph Anton Mitterer <mail@christoph.anton.mitterer.name>

shell/key-bindings.fish

@@ -11,7 +11,7 @@
 # - $FZF_ALT_C_COMMAND
 # - $FZF_ALT_C_OPTS
 
-if status is-interactive
+status is-interactive; or return 0
 
 
 # Key bindings
@@ -173,6 +173,3 @@ function fzf_key_bindings
   end
 
 end
-
-
-end